Double ring network system and communication control method thereof, and transmission station, and program for transmission stations

ABSTRACT

A double ring network system configured with two or more transmission stations each including a pair of bi-directionally communicative communication ports, including any adjacent two transmission stations as terminal stations, and any transmission station as a base, as mutually connected in a ring form by communication ports through a transmission line, for intercommunications between transmission stations, in which the transmission stations are each adapted to determine whether or not frame signals are received from adjacent transmission stations, transmit route identifying frame signals for identification of routes to adjacent transmission stations, when having failed in reception, and set own station as a terminal station substituting for a current terminal station, when having received no responses to the route identifying frames from adjacent transmission stations, so they are kept from arriving at ring-like connected subsequent transmission stations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 12/515,322,filed May 18, 2009, the entire content of which is incorporated hereinby reference. U.S. application Ser. No. 12/515,322 is a National Stageof PCT/JP07/055,292, filed Mar. 15, 2007, and claims the benefit ofpriority under 35 U.S.C. §119 of Japanese Application 2006-311274, filedNov. 17, 2006.

TECHNICAL FIELD

The present invention relates to a double ring network system includinga plurality of transmission stations mutually connected in the form of aring through communication lines adapted for bi-directionalcommunications, the transmission stations normally each sendingtransmission frames in both directions of the ring simultaneously, thetransmission frames being received and repeated by respectivetransmission stations, permitting intercommunications to be therebyimplemented with all transmission stations in the ring.

In particular, it addresses a control system including a pair ofadjacent transmission stations adapted as terminal stations forprohibiting bi-directionally repeating transmission frames to keep senttransmission frames from continuing circulation along the ring, forconfiguration of a double ring network being a ring form but equivalentto a bus type.

Still more, it addresses a redundant control system adapted, with anevent of one-point trouble in the double ring network, to havetransmission stations paired at new locations, out of transmissionstations with maintained sound functions, alter into terminal stations,in order to avoid an entire shutdown.

Yet more, it addresses a control of configuration for double ringnetworks having data frames and interfaces compliant with theISO/IEC8802-3 Ethernet® standard, to be employed in applications ortransmission frames being transmitted among the transmission stationsand associated with the control systems, and adapted as a physical layerin terms of an OSI (ISO/IEC7498-1) physical layer to be free fromrestrictions to the data link layer as an upper layer, in particular tomedia access control systems (MAC) implementing an access control ofcommon transmission line to avoid collision between transmission frameson a common transmission line.

BACKGROUND ART

Generally, for a plurality of transmission stations mutually connectedin turn in the form of a ring through communication lines capable ofbi-directional communications to constitute a network system, thetransmission stations are each adapted to send transmission frames inboth directions.

Those transmission stations are each adapted for one of presettransmission stations to work as a control station, so that transmissionframes sent from respective transmission stations are kept fromcontinuing circulation in the ring.

As a conventional example of this system cutting a transmission frameflow at a transmission station, we have Japanese Patent Publication No.3,461,954 (patent document 1).

In this Patent document 1, if a trouble happens at any single locationwhile running, this transmission station operates as a central controlstation for interactions with transmission stations in a network, mainlyin particular with those transmission stations which have detected thetrouble, to cut off a part in trouble.

Or, having a trouble determined from a break in a steadyintercommunication by transmission frame, it cuts off a part in trouble,and implements a bi-directional repeating of transmission frame that ithas cut till then as a control station, which is done as a system toavoid an entire shutdown of network system due to one-point trouble.

There is also an IEEE 802.5 token ring system network, as a similarsystem.

On the other hand, there is an ANSI X3T 9.5 FDDI as a ring form network,in which transmission stations are normally each adapted to sendtransmission frames in a direction on a ring, and a respectivetransmission station is adapted to repeat transmission frames sent fromother transmission stations, and any transmission frame that has comearound through the ring is dropped at the station where it has beensent, thereby keeping the transmission frame from continuing circulationin the ring.

This type of network has communication lines mutually permitting abi-directional communication, and normally employs a communication linefor one direction, with a communication line for the other directionheld in a waiting state.

If a trouble happens at any single location while running, transmissionframes are to be blocked there, whereto a predetermined centraltransmission station interacts mainly with transmission devices adjacentto the location of trouble, to have a communication line fold back atthe adjacent paired transmission stations with a troubled part inbetween, so a reverse directional communication line that has been in awaiting state till then revives to constitute a new ring network, whilehaving a communication line doubled in length. It is thereby avoided toundergo an entire shutdown of network due to one-point trouble.

Like this, it is typical for examples in the past to block atransmission flow at a stationary single point in a ring form network.

The point to be blocked is at a central control station fixedlydetermined in advance, or such a transmission station that istemporarily given a transmission right to send transmission frames on acommon transmission line, as it can stand as a control station tocontrol the transmission line, while holding the transmission right.

Further, there is disclosure (patent document 2) of a data transmissionprocessing system in which an application program for a respective datatransmission device is sent from a single point, and respectivetransmission devices are remote-controlled for maintenance from thesingle point, allowing for an improved maintenance work efficiency andwork saving.

-   Patent document 1: Japanese Patent Publication No. 3,461,954-   Patent document 2: Japanese Patent Application Laid-Open Publication    No. 5-289968

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, in those network systems, if a trouble happens at one location,a procedure (for a transmission line control system specific to eithernetwork is followed, for a control station and transmission stationsadjacent to the trouble location to determine the timing ofcommunications in between, or for synchronization, to fold back withinthe control station where it has been cut in the former case, or at twopoints with the trouble location in between in the latter case, to avoidan entire shutdown, keeping transmission frames from continuingcirculation.

Either system depends on the transmission line control system, andundergoes issues including, among others, a limited versatility, and arequired time for control to recover from trouble even if it is applied.

Therefore, it has been difficult to provide a bus type transmission lineindependently of the transmission control system, as a universal systemto one-point trouble, as an issue.

Further, the patent document 1 is a measure to fold back for occurrenceof a disconnection between a node (transmission station) and atransmission station. Instead, disconnection does not always occur atone point, there may be two points of disconnection. To this point, thepatent document 1 presumes one-point disconnection, and for two pointsof disconnection, lacking facile measures, it needs a worker to go thesites to determine terminal stations.

Further, a recovery from disconnection at one point may be followed bydisconnection at another point. In such a case, it is desirable forterminal stations to automatically switch.

Therefore, it has been a desideratum to provide a double ring networksystem of a bus type in which terminal stations can be automatically setto stop circulation of transmission frame, irrespective of the number.

Further, the patent document 2 provides an updating method forapplication programs, where programs are updatable from a datatransmission device of a single point connected to a transmission line,whereas for update of firmware, the transmission device needs newfirmware to be installed before a restart, which requires labor work tobring the device once in a state of shutdown to restart as hardware.However, this operation may be impracticable, and update of firmware maybe disabled. Therefore, for a new terminal station to be set, firmwarehas to be updated, with a cost.

The present invention has been devised in view of such issues, and it isan objective to provide a double ring network system including aplurality of (odd or even) transmission stations connected through atransmission line, as a double ring network system of a bus type, not acycloid, that has right-handed terminal station and left-handed terminalstation automatically determined.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is diagram describing positional relation between a masterstation and both terminal stations in a double ring network system afterinitialization.

FIG. 2 is diagram describing a set of transmission stations mutuallyconnected by a bi-directional transmission line in a double ring networksystem.

FIG. 3 is diagram of a hardware configuration constituting an embodimentexample (the 1^(st)) of a configuration of transmission station fordouble ring network systems.

FIG. 4 is diagram of a hardware configuration constituting an embodimentexample (the 2^(nd)) of a configuration of transmission station fordouble ring network systems.

FIG. 5 is a diagram describing status of switches at both terminalstations after initialization.

FIG. 6 shows status of switches and modes at a respective station at atime of startup of initialization.

FIG. 7 is a diagram describing conditions of actions at normal stationsand both terminal stations after initialization.

FIG. 8 is a diagram describing transition of station modes from a startof initialization.

FIG. 9 is a sequence chart of an embodiment example (the 1^(st)) of INZframe intercommunications between transmission stations at a time ofinitialization.

FIG. 10 is a flowchart describing an initializing process (the 1^(st))at a #STj transmission station.

FIG. 11 is a flowchart describing the initializing process (the 1^(st))at the #STj transmission station.

FIG. 12 is a sequence chart of an example (the 1^(st)) ofintercommunications between transmission stations at a time ofinitialization (for transmission stations ST1, ST2, and ST8).

FIG. 13 is a sequence chart of the example (the 1^(st)) ofintercommunications between transmission stations at a time ofinitialization (for transmission stations ST1, ST2, and ST8).

FIG. 14 is a sequence chart of an embodiment example (the 2^(nd)) of INZframe intercommunications between transmission stations at a time ofinitialization.

FIG. 15 is a sequence chart of an initializing process (the 2^(nd)) at a#STj transmission station.

FIG. 16 is a sequence chart of the initializing process (the 2^(nd)) atthe #STj transmission station.

FIG. 17 is a sequence chart of an example (the 2^(nd)) ofintercommunications between transmission stations at a time ofinitialization (for transmission stations—ST1, ST2, and ST8).

FIG. 18 is a sequence chart of the example (the 2^(nd)) ofintercommunications between transmission stations at a time ofinitialization (for transmission stations—ST1, ST2, and ST8).

FIG. 19 is a diagram describing an exemplary occurrence of transmissionanomaly between #ST10 and #ST9.

FIG. 20 is a diagram describing status of switches at respectivestations by reception anomaly detection and no-SYN detection after theoccurrence of transmission anomaly between #ST10 and #ST9.

FIG. 21 is a sequence chart describing an example (the 1^(st)) ofreconfiguration from a one-point trouble of a double ring networksystem.

FIG. 22 is a sequence chart describing an example (the 2^(nd)) ofreconfiguration from a one-point trouble of a double ring networksystem.

FIG. 23 is a diagram describing a format of ISO/IEC 8802-3 Ethernet®transmission frame.

FIG. 24 is a flowchart describing an outline of an automatic terminalstation setting function of a double ring network system according tothis embodiment.

FIG. 25 is a diagram describing a terminal station setting in an initialphase.

FIG. 26 is a diagram describing an exchange of terminal stations.

FIG. 27 is a diagram of schematic configuration of transmissionstations.

FIG. 28 is a diagram of schematic configuration describing aninitializing process according to this embodiment.

FIG. 29 is a chart of sequences in an initializing process according tothis embodiment.

DESCRIPTION OF REFERENCE CHARACTERS

-   1 transmission station (# ST1)-   2 transmission station (# ST2)-   3 transmission station (# ST3)-   4 transmission station (# ST4)-   5 transmission station (# ST5)-   6 transmission station (# ST6)-   7 transmission station (# ST7)-   8 transmission station (# ST8)-   10 communication port section-   11 communication port section-   12 repeater A (FW-A)-   18 reception permitting switch (SW-RVC-A)-   31 frame detecting determiner-   32 reception anomaly detecting circuit (RCV-ERR-A)-   34 SYN frame detecting circuit (SYN-DET-A)-   37 RRR frame reception detecting circuit (RRR-DET-A)-   38 RRR frame destination address holding circuit (RRR-RCV-ASDRS)

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment Claim 1

This is a control method for double ring networks including a set of twoor more transmission stations each respectively configured with a pairof communication ports for communications to be implementedbi-directionally, and mutually connected by said pairs of communicationports thereof in a ring form through a transmission line to implementintercommunications between transmission stations, characterized

for the respective transmission station, by:

a step of simultaneously sending transmission frames containinginformation at a time from paired communication ports of saidtransmission station;

a step of detecting a transmission frame sent from another said transfission station received at one of said paired communication ports; and

a step of sending above-noted said transmission frame as repeatable toanother communication port being the other with respect to the onecommunication port, from said other communication port, and

for a respective one of adjacent paired said transmission stations outof said set of two or more transmission stations mutually connected inthe ring form, by: a step of having the transmission frame sent from onesaid transmission station's communication port; and

a step of performing, for a transmission frame received at the othersaid transmission station's communication port as it is connectedthrough the transmission line, a detection at this station, and

in that said transmission frame to be responded in accordance withinformation contained in said transmission frame is kept from beingsent, through a repeating from said receiving communication port to theother communication port, from said other communication port,

whereby said received transmission frame is kept from arriving atring-form connected and subsequent transmission stations in a repeatingdirection thereof, and above-noted transmission frames sent from saidtransmission station are kept from circulating in a network configuredin the ring form.

Second Embodiment Claim 2

This is the control method for double-ring networks according to theembodiment 1 (claim 1), characterized

for the set of transmission stations, by:

having, at a respective one of adjacent paired said transmissionstations out of said set of two or more transmission stations mutuallyconnected in the ring form in positions determined relative to one saidtransmission station as a base in accordance with a total number of saidtransmission stations constituting the network of the ring form and atotal length of the transmission line connecting said transmissionstations with each other, the transmission frame sent from one saidtransmission station's communication port.

Third Embodiment Claim 3

This is the control method for double-ring networks according to theembodiment 1 (claim 1) or the embodiment 2 (claim 2), wherein

as for a format of said transmission frame to be sent and receivedthrough said communication ports, and a transmission line interface ofsaid communication ports, it complies with the ISO/IEC8802-3 standard.

Fourth Embodiment Claim 4

This is an initializing method for double ring networks including a setof two or more transmission stations each respectively configured with apair of communication ports for communications to be implementedbi-directionally, and mutually connected by said pairs of communicationports thereof in a ring form through a transmission line to implementintercommunications between transmission stations, comprising:

for a base transmission station being one said transmission station as abase out of said set of two or more transmission stations mutuallyconnected in the ring form,

a step of sending periodically initialization-instructing transmissionframes (INZ frames) in both directions;

for a respective transmission station receiving and detecting this,

a step of turning repeat of transmission frame from a communication porton this as-having-received side to a communication port on the otherside, from a prohibiting state to a permitting state; and

a step of permitting reception and take-in of transmission framethereafter at the communication port on the as-having-received side, andsending an INZ frame as a responding acknowledgment (a respondingacknowledgment INZ frame) at the as-having-received communication portside, as a response for reception acknowledgment; further

a step of responding to reception and detection, as following thesending the INZ frame, of a said above-noted responding acknowledgmentINZ frame from a one-adjacent transmission station in a repeatingdirection from said above-noted communication port having first receivedan INZ frame to the other communication port, by turning repeat oftransmission frame from a communication port on this as-having-receivedside to a communication port on the other side, from a prohibiting stateto a permitting state; and

a step of permitting reception and take-in of transmission framethereafter at the communication port on that as-having-received side,whereby at this transmission station thereafter reception and take-in oftransmission frames to be received at communications ports onbi-directional sides and repeat thereof to the other sides are enabled;further

for a respective one of a transmission station in a position to receiveabove-noted INZ frames at communication ports on both sides, and atransmission station in a position adjacent to that transmission stationthrough a transmission line, as they are determined in accordance with atotal number of said transmission stations constituting the network inthe ring form, and a total length of the transmission line connectingsaid transmission stations with each other,

a step of having a transmission frame sent from one said transmissionstation's communication port and received at said other transmissionstation's opposing communication port, detected at this transmissionstation; and

for said transmission frame to be responded in accordance withinformation contained therein, setting repeat from saidas-having-received communication port to the other communication port toa permitting state, wherein

they are configured as terminal stations also for reception and take-into be prohibited, whereby at a respective one of these terminal stationsno transmission frame received from the other terminal station isrepeated to send to ring-form connected and subsequent transmissionstations in a repeating direction thereof, and transmission frames sentfrom respective said transmission stations are kept from circulating ina network configured in the ring form.

Fifth Embodiment Claim 5

This is the initializing method for double-ring networks according tothe embodiment 4 (claim 4), comprising:

for said transmission station being one said transmission station as abase out of said set of two or more transmission stations mutuallyconnected in the ring form, a step of sending initialization-instructingtransmission frames (INZ frames) in both directions;

for a transmission station one-adjacent to said transmission stationhaving received and detected this, a step of turning repeat oftransmission frame from a communication port on this as-having-receivedside to a communication port on the other side, from a prohibiting stateto a permitting state; and

a step of permitting reception and take-in of transmission framethereafter at the communication port on the as-having-received side; and

a step of sending INZ frames as a responding acknowledgment (respondingacknowledgment INZ frames) addressing a source address of said receivedINZ frame as a destination, in both directions, as a response forreception acknowledgment; further

a step of responding to reception and detection, as following thesending the INZ frame, of a said above-noted responding acknowledgmentINZ frame of a one-adjacent transmission station addressing own station,from said one-adjacent transmission station in a repeating directionfrom said above-noted communication port having first received an INZframe to the other communication port, by turning repeat of transmissionframe from a communication port on this as-having-received side to acommunication port on the other side, from a prohibiting state to apermitting state, wherein

reception and take-in of transmission frame are permitted thereafter atthe communication port on that as-having-received side, whereby at thistransmission station thereafter reception and take-in of transmissionframes to be received at communications ports on both sides and repeatthereof to the other sides are enabled, and

beginning from said above-noted transmission station as a base havingsent INZ frames in both directions, sequentially on respectivetransmission stations in positions in both directions of the ring form,reception of an INZ frame is responded by again sending INZ frames atcommunications ports on both sides,

a step of thereby determining in accordance with a total number of saidtransmission stations constituting the network in the ring form, and atotal length of the transmission line connecting said transmissionstations with each other,

a transmission station in a position to receive INZ frames atcommunication ports on both sides, and a transmission station in aposition adjacent to that transmission station through a transmissionline; for a respective one of which

a step of having a transmission frame sent from one said transmissionstation's communication port and received at said other transmissionstation's opposing communication port, detected at this transmissionstation, and for said transmission frame to be responded in accordancewith information contained therein, setting repeat from saidas-having-received communication port to the other communication port toa permitting state, wherein

they are configured as terminal stations also for reception and take-into be prohibited, whereby at a respective one of these terminal stationsno transmission frame received from the other terminal station isrepeated to send to ring-form connected and subsequent transmissionstations in a repeating direction thereof, and transmission frames sentfrom respective said transmission stations are kept from circulating ina network configured in the ring form.

Embodiment 6 Claim 6

This is the initializing method for double-ring networks according tothe embodiment 5 (claim 5), comprising:

for a respective transmission station, a step of responding to an INZframe it has first received in an initializing interval by holding, asan address of an adjacent transmission station opposing on thisas-having-received communication port (an MS port) side, a sourceaddress in said received INZ frame together with an identifier of saidreception port; and

a step of successively sending INZ frames addressing the address of saidadjacent transmission station as a destination in both directions,wherein

following said sending, within a prescribed time, if an INZ frameaddressing own station as a destination is received at a communicationport on an opposite side to the MS port, then as being an above-notedresponding acknowledgment INZ frame from an adjacent transmissionstation opposing this communication port side,

a source address in this INZ frame is held together with an identifierof this reception port, whereby addresses of the respective transmissionstations adjacent on both sides of this transmission station can beacquired.

Embodiment 7 Claim 7

This is the initializing method for double-ring networks according tothe embodiment 4 (claim 4), the embodiment 5 (claim 5), or theembodiment 6 (claim 6), wherein

at a time when above-noted said two terminal stations are adjacentlyconfigured in positions determined in accordance with a total number ofsaid transmission stations constituting the network in the ring form,and a total length of the transmission line connecting said transmissionstations with each other, with said one transmission station as a base,or

at a time when they are set as terminal stations by absence of receptionof responding acknowledgment INZ frames from adjacent transmissionstation of own station in way of initialization,

a respective one of the two terminal stations of the double ring networksends an INZ-COMP frame containing an indication of completion ofinitialization, and terminal station information including a terminalstation address and a terminal station mode, or said INZ-COMP frame isreceived and detected at said one transmission station as a base,whereby

a completion of initialization of the double ring network can beverified.

Embodiment 8 Claim 8

This is a transmission station for double-ring networks including a setof two or more transmission stations each respectively configured with apair of communication ports for communications to be implementedbi-directionally, and mutually connected by said pairs of communicationports thereof in a ring form through a transmission line to implementintercommunications between transmission stations, characterized

in a complete state of initialization, for each of one or more saidtransmission stations, by: means for periodically sending one or moretransmission frames each respectively containing specific information;

for the respective transmission station configured to receivetransmission frames through said pair of communication ports being A andB respectively (these two communication ports (are referred herein tocommunications ports A, and -B. And, means, functions, etc relating tosending and receiving a transmission frame through the communicationport A shall be referred to by adding suffix -A, and likewise, what isto the communication port B, by suffix -B), by: “SYN frame detectingmeans A, and -B” for detecting, out of said periodically senttransmission frames, SYN frames having specific information meeting setconditions (referred herein to a SYN frame each), respectively; “no-SYNdetecting means A, and -B” for detecting no reception of said SYN framesover a preset interval, from output signals of said SYN frame detectingmeans A, and -B, respectively; “SYN absence detecting means” fordetecting, under a condition of periodic SYN frame arrivals through onecommunication port being consecutively continued, absence of periodicarrivals through the other communication port consecutive over a presetinterval; and “reception anomaly detecting means A, and -B” fordetecting anomalies in states of reception signals of transmissionframes received through the communication ports, respectively, and meansfor having a transmission frame as received through either communicationport -A or -B as having detected a no-SYN detecting state by the no-SYNdetecting means A or -B, detected and verified, and responded inaccordance with information contained in said transmission frame, andchanging either as-having-received communication port (as thecommunication port A) to “a blocked state” for said transmission frameto be kept from being repeated to the other communication port (thecommunication port B) to send from the other communication port (thecommunication port B) (On the other hand, as used herein, “an unblockedstate” refers to a state of communication port adapted for atransmission frame to be repeated from an as-having-receivedcommunication port to the other communication port to send from theother communication port.); and

changing the communication port A or -B as having detected a receptionanomaly detecting state by the reception anomaly detecting means A or-B, to a blocked state, thereby holding communication ports of aplurality of transmission stations unblocked, on a way from a detectionof failure occurrence to a network function recovery by a recoveryprocedure, and in that: the above-noted functions of said terminalstation are fulfilled at the plurality of transmission stations.

Embodiment 9 Claim 9

This is a reconfiguration method in anomaly occurrence for double ringnetworks including a set of two or more transmission stations eachrespectively configured with a pair of communication ports forcommunications to be implemented bi-directionally, and mutuallyconnected by said pairs of communication ports thereof in a ring formthrough a transmission line to implement intercommunications betweentransmission stations, characterized

in a state of configuration for transmission frames to be kept fromcontinuing circulation in the network of the ring form, by two adjacentterminal stations, with the initialization completed, under a conditionthat one or more said transmission stations are compliant with aspecifically undefined transmission line control system for avoidingcollisions between transmission frames on double ring networks (MAC), tosend specific information-containing one or more transmission frames tobe periodically sent and, among others, above-noted said SYNN frames,and transmission frames to be sporadically sent, wherein

the respective transmission station comprises:

“RRR frame reception detecting means A, and -B” for detecting receptionof transmission frames containing specific control information (referredherein to an RRR frame each), respectively;

“own address setting” means for setting information for identificationof own station;

“adjacent station address setting means A, and -B” for settinginformation for identification of transmission stations adjacent tocommunication ports A, and -B, respectively;

“address match detecting means” for detecting a match by comparisonbetween identification information of own station and destinationinformation in a received RRR frame from a reception output of eitherRRR frame reception detecting means;

“blocked port resetting means” for responding to a match output of theaddress match detecting means by changing a communication port havingreceived said RRR frame (referred herein to an RRR reception port) to anunblocked state;

“RRR reception responding means” for responding to a mismatch output ofthe address match detecting means by reading identification informationof an adjacent transmission station corresponding to the RRR receptionport from either adjacent station address setting means, to have as adestination to be addressed, and sending an RRR frame generated with thedestination, through the RRR reception port, immediately in time forcompletion of reception of the RRR frame; and

“RRR responding acknowledgment means” for detecting by checking forreception of an RRR frame addressing own station as a destination,within a preset time, following said sending said RRR frame,

as an anomaly has occurred in a transmission line or at a transmissionstation on a route from a transmission station for sending SYN frames(referred herein to a synchronizing station), this transmission stationbeing inclusive, with terminal stations inclusive, for a respectivetransmission station on ways from a location of occurrence of anomaly tothe terminal stations, by a step of detecting an anomalous state by saidno-SYN detecting means and said reception anomaly detecting means inresponse to the occurrence of anomaly, and

for a respective transmission station adjacent to the location ofoccurrence of anomaly on routes from the location of occurrence ofanomaly to the synchronizing station, by a step of detecting ananomalous state by the reception anomaly detecting means, wherein

as-having-detected communication ports have their status turned toblocked states, respectively, and between said terminal stations beingtwo, for one terminal station in a subsequent position on a route fromthe synchronizing station to the location of occurrence of anomaly, by astep of determining at this terminal station (referred herein to a SYNabsence detecting terminal station) an anomaly as having occurred on theroute to the synchronizing station, from a detection output of theanomalous state by said SYN absence detecting means and a no-SYNdetection output of the SYN absence detecting means, and

for the other terminal station (referred herein to a SYN normal terminalstation), which continuous receiving SYN frames normally, by a step ofdetermining a route from this SYN normal terminal station to thesynchronizing station as having a maintained normal communicationfunction,

for the SYN absence detecting terminal station, by

a step of responding to a detection of occurrence of anomaly of a stateof SYN absence from the SYN absence detecting and no-SYN detectingmeans, by immediately sending RRR frames addressing the SYN normalterminal station as a destination, through the communication port A, and-B, and

a step of waiting, at the RRR responding acknowledgment means, for aresponse from a transmission station adjacent on an opposite side to theSYN normal terminal station,

for the SYN normal terminal station, by a step of responding toreception of an RRR frame from the SYN absence detecting terminalstation, as own station is a destination, by changing an RRR receptionport that has been in a blocked state as a terminal station, to anunblocked state by said blocked port resetting means,

as the terminal station status is cancelled, for a respectivetransmission station functioning normally on a way from the SYN absencedetecting terminal station to the location of occurrence of anomaly, bya step of responding to reception of an RRR frame from the SYN absencedetecting terminal station, as being not a destination, by sending anRRR frame having as a destination an adjacent transmission station onthe way to the SYN absence detecting terminal station, by said RRRreception responding means, through an RRR reception port, immediatelyafter a completion of reception of the RRR frame.

for the SYN absence detecting terminal station, by a step of respondingto reception in time of an RRR frame addressing own station from anadjacent station on the way to the synchronizing station, by the RRRresponding acknowledgment means, by changing a communication port thathas been in a blocked state since the time of anomaly detection, to anunblocked state, and

a step of following this changing to change, after lapse of a time theRRR responding acknowledgment means has preset, also the othercommunication port that has been blocked since before as a terminalstation, to an unblocked state, thereby canceling the terminal stationstatus,

for the respective transmission station functioning normally on the wayfrom the SYN absence detecting terminal station to the location ofoccurrence of anomaly, by a step of responding to acknowledgment ofreception of an RRR frame addressing own station from the adjacentstation on the way to the synchronizing station, by the RRR respondingacknowledgment means, by changing a communication port that has been ina blocked state since the time of anomaly detection, to an unblockedstate,

for a respective transmission station adjacent to the location ofoccurrence of anomaly on ways to SYN absence detecting terminalstations, by a step of following absence of reception of an RRR frameaddressing own station over lapse of a preset time, by the RRRresponding acknowledgment means, to hold a communication port as it isblocked, to function as a new terminal station, and

for occurrence of anomaly at a location adjacent to a SYN absencedetecting terminal station, likewise followed by absence of reception ofan RRR frame addressing own station over lapse of a preset time, by theRRR responding acknowledgment means, by a step of holding acommunication port that has been in a blocked state since the time ofanomaly detection, as it is blocked, and in that

the other communication port that has been in a blocked state sincebefore as a terminal station is changed to an unblocked state, and asnew terminal stations, a terminal station on a way from the anomalyoccurrence location to the synchronizing station, and a terminal stationon an opposite way from the anomaly occurrence location are changed tobe new double ring network's terminal stations, whereby a network of thering form is re-configured upon occurrence of communication anomaly.

Embodiment 10 Claim 10

This is the reconfiguration method in anomaly occurrence for double-ringnetworks according to the embodiment 9 (claim 9), characterized

in a state of configuration for transmission frames to be kept fromcontinuing circulation in the network of the ring form, by two adjacentterminal stations, with the above-noted said initialization completed,under a condition that one or more said transmission stations arecompliant with a specifically undefined transmission line control systemfor avoiding collisions between transmission frames on double ringnetworks, to send specific information-containing one or moretransmission frames to be periodically sent and, among others,above-noted said SYNN frames, and transmission frames to be sporadicallysent, wherein

respective transmission station comprises “own address setting” meansfor setting information for identification of own station, and “adjacentstation address setting means A, and -B” for setting information foridentification of transmission stations adjacent to communication portsA, and -B, respectively,

as an anomaly has occurred in a transmission line or at a transmissionstation on a route from a transmission station for sending SYN frames(referred herein to a synchronizing station), this transmission stationbeing inclusive, with terminal stations inclusive, for a respectivetransmission station on ways from a location of occurrence of anomaly tothe terminal stations, by means for detecting an anomalous state by saidno-SYN detecting means and said reception anomaly detecting means inresponse to the occurrence of anomaly, and

for a respective transmission station adjacent to the location ofoccurrence of anomaly on routes from the location of occurrence ofanomaly to the synchronizing station, by means for detecting ananomalous state by the reception anomaly detecting means, wherein

as-having-detected communication ports have their status turned toblocked states, respectively, and between said terminal stations beingtwo, for one terminal station in a subsequent position on a route fromthe synchronizing station to the location of occurrence of anomaly, bymeans for determining at this terminal station (referred herein to a SYNabsence detecting terminal station) an anomaly as having occurred on theroute to the synchronizing station, from a detection output of theanomalous state by said SYN absence detecting means and a no-SYNdetection output of the SYN absence detecting means, and

for the other terminal station (referred herein to a SYN normal terminalstation), which continuous receiving SYN frames normally, by means fordetermining a route from this SYN normal terminal station to thesynchronizing station as having a maintained normal communicationfunction,

for the SYN absence detecting terminal station, by means for monitoringa sequence of transmission frames received from the SYN normal terminalstation, sending specific control information-containing transmissionframes (referred herein to an RRR frame each) addressing the SYN normalterminal station as a destination, at sending timings of transmissionframes assigned to own station in compliance with a transmission linecontrol system for avoiding collisions between transmission frames ondouble ring networks, through the communication port A, and -B, andwaiting for reception of an RRR frame addressing own station as adestination from an adjacent station on the way to the synchronizingstation,

for the SYN normal terminal station, by means for responding toreception of an RRR frame from the SYN absence detecting terminalstation, by comparing own station identification information withdestination information in the received RRR frame, and

for a result of this comparison that own station is the destination, bymeans for changing a communication port having received said RRR frame(referred herein to an RRR reception port) that has been in a blockedstate since before as a terminal station, to an unblocked state,canceling the terminal station status,

for a respective transmission station functioning normally on a way fromthe SYN absence detecting terminal station to the location of occurrenceof anomaly, by means for responding to reception of an RRR frame fromthe SYN absence detecting terminal station, by comparing own stationidentification information with destination information in the receivedRRR frame, and

for a result of this comparison as being not the destination, by meansfor sending an RRR frame having as a destination an adjacenttransmission station on the way to the SYN absence detecting terminalstation, by said RRR reception responding means, through an RRRreception port, immediately after a completion of reception of the RRRframe,

for the SYN absence detecting terminal station, by means for respondingto reception within a preset time of an RRR frame addressing own stationfrom an adjacent station on the way to the synchronizing station, bychanging a communication port that has been in a blocked state since thetime of anomaly detection, to an unblocked state, and

means for following this to change, after lapse of a time the RRRresponding acknowledgment means has preset, also the other communicationport that has been blocked since before as a terminal station, to anunblocked state, canceling the terminal station status,

for the respective transmission station functioning normally on the wayfrom the SYN absence detecting terminal station to the location ofoccurrence of anomaly, by means for responding to acknowledgment ofreception within a preset time of an RRR frame addressing own stationfrom the adjacent station on the way to the synchronizing station, bychanging a communication port that has been in a blocked state since thetime of anomaly detection, to an unblocked state,

for a respective transmission station adjacent to the location ofoccurrence of anomaly on ways to SYN absence detecting terminalstations, by means for following absence of reception of an RRR frameaddressing own station over lapse of a preset time, by the RRRresponding acknowledgment means, to hold a communication port as it isblocked, to function as a new terminal station, and

for occurrence of anomaly at a location adjacent to a SYN absencedetecting terminal station, likewise followed by absence of reception ofan RRR frame addressing own station over lapse of a preset time, bymeans for holding a communication port that has been in a blocked statesince the time of anomaly detection, as it is blocked, and in that

the other communication port that has been in a blocked state as aterminal station is changed to an unblocked state, and as new terminalstations, a terminal station on a way from the anomaly occurrencelocation to the synchronizing station, and a terminal station on anopposite way from the anomaly occurrence location are changed to be newdouble ring network's terminal stations, whereby a network of the ringform is re-configured upon occurrence of communication anomaly.

Embodiment 11 Claim 11

The reconfiguration method in anomaly occurrence for double-ringnetworks according to according to the embodiment 9 (claim 9) and theembodiment 10 (claim 10), wherein,

as for a format of said transmission frame to be sent and receivedthrough said communication ports, and a transmission line interface ofsaid communication ports, it complies with the ISO/IEC8802-3 standard.

This is. The embodiments will be described.

FIG. 2 is a schematic diagram of configuration of a double ring networksystem (referred herein sometimes simply to a double ring network) towhich the present invention is applicable.

FIG. 2 includes eight transmission stations (transmission stations 1 to8), which are mutually connected through a bi-directional transmissionline to constitute a ring form network, as illustrated in FIG. 2. InFIG. 2, transmission station 1 is labeled as #ST1, transmission station2, as #ST2, transmission station 3, as #ST3, transmission station 4, as#ST4, transmission station 5, as #ST5, transmission station 6, as #ST6,transmission station 7, as #ST7, and transmission station 8, as #ST8, toindicate their station addresses on the network.

To the embodiment 1 (claim 1), FIG. 1 gives an example of so-calleddouble ring network system in the invention. In the example of FIG. 1,transmission station 1 (#ST1) serves as a master station (MS), andtransmission station 5 (#ST5) as well as transmission station 6 (#ST6)stands as a terminal station. That one which is first powered on tostart serves as the master station.

In FIG. 1, transmission stations being eight in total are mutuallyconnected like the double ring network system in FIG. 2, while in thedouble ring network system according to this invention, eachtransmission station has an own station automatic terminal stationfunction as described, which is not given in the double ring networksystem in FIG. 2.

The own station automatic terminal station function allows for atransmission frame sent from one transmission station's communicationport and received at the other transmission station's communication portconnected thereto through a transmission line to be detected at thetransmission station, and responded in accordance with informationcontained in the transmission frame, while it is kept from beingrepeated from the communication port where it is received to the othercommunication port.

Therefore, as a terminal station given a function not to send thetransmission frame from the other communication port, the transmissionstation 5 (#ST5) constituting a terminal station ST-T-L, and thetransmission station 6 (#ST6) constituting a terminal station ST-T-R areincorporated in the configuration as a pair.

It therefore is possible for transmission frames sent from transmissionstations to be kept from being circulated in the network systemconfigured in a ring form.

It is noted that in FIG. 1 #ST5 and #ST6 are labeled with terminalstation ST-T-L and terminal station ST-T-R, respectively, which is in noway restrictive in the network configuration of FIG. 1.

That is, FIG. 1 is a double ring network system including a set of twoor more transmission stations each configured with a pair ofcommunication ports for communications to be implementedbi-directionally, and mutually connected by their pairs of communicationports in a ring form through a transmission line to implementintercommunications between transmission stations.

The transmission stations are each adapted to simultaneously sendtransmission frames containing information at a time from twocommunication ports to adjacent transmission stations.

Further, they are each adapted to detect a transmission frame sent fromanother transmission station and received at one of two communicationports, repeat it to the other communication port, and send thetransmission frame from the other communication port.

A respective one of adjacent two transmission stations out of the set oftwo or more transmission stations mutually connected in the ring form isadapted to detect, at the transmission station, a transmission framesent from one transmission station's communication port under alater-described specific condition and received at the othertransmission station's communication port as it is connected through thetransmission line, while the transmission frame is responded inaccordance with information contained in the transmission frame, it iskept from being repeated from the communication port where it isreceived to the other communication port.

That is, whether odd or even in number, if the specific condition ismet, the transmission frame is kept from being sent from the othercommunication port, whereby it is kept from arriving at ring-formconnected and subsequent transmission stations in a repeating directionthereof, so transmission frames sent from transmission stations can bekept from circulating in a network configured in the ring form.

For the embodiment 2 (claim 2), providing #ST1 shown in FIG. 1 as amaster station, relative to the #ST1 as a base, #ST5 and #ST6 areuniquely determined as terminal stations depending on the number oftransmission stations (eight in this case) and the length oftransmission line through the transmission stations.

Although specific determination procedures may vary depending on claim4, claim 5, and embodiment examples thereof, the position of terminalstation to be set is a respective one of adjacent transmission stationson the opposite side of the ring in view of a transmission stationselected as the master station, and located about a count number of halfthe total transmission station number as it is counted from the masterstation.

That is, by configuration of terminal stations in positions determinedrelative to the master station, transmission frames sent fromtransmission stations can be kept from circulating in a networkconfigured in a ring form.

That is, like FIG. 1, there is a plurality of transmission stations eachrespectively provided with a pair of communication ports and mutuallyconnected in a ring form to constitute a double ring network system.Again, at a respective transmission station, transmission frames aresimultaneously sent at a time from the paired communication ports, and atransmission frame from another transmission station is received at onecommunication port, where it is detected, and repeated to the othercommunication port, and sent from the other communication port.

And, there are terminal stations set as adjacent paired transmissionstations out of a set of two or more transmission stations mutuallyconnected in a ring form, in positions (odd umber or even numberinclusive) determined relative to one transmission station as a base, inaccordance with a total number of transmission stations constituting thenetwork of the ring form and a total length of the transmission lineconnecting the transmission stations with each other, of which arespective transmission station is adapted to detect, at thetransmission station, reception of a transmission frame sent from onetransmission station's communication port and received at the othertransmission station's communication port as it is connected through thetransmission line. Further, the transmission stations set as terminalstations are each adapted to provide a response in accordance withinformation contained in the transmission frame, but not for any repeatfrom the communication port where it is received to the othercommunication port.

Therefore, at the respective transmission station set as a terminalstation, the transmission frame is kept from being sent from the othercommunication port, whereby it is kept from arriving at ring-formconnected and subsequent transmission stations in a repeating directionthereof, so transmission frames sent from transmission stations can bekept from circulating in the network configured in the ring form.

The embodiment 3 (claim 3) allows for dominances in, among others,convenient utilization or incorporation such as of network components,accessories, or media converters, or interfacing devices, or testtesting devices, such as in or for transmitter or receiver IC's, datatransmission reception LSI's or circuit components remarkable inperformance enhancement and price decline, as well as in consistency andpractical profit such as those with or by communication protocolextension procedures, protocol processing firmware or middleware, orgeneral-purpose IT application software programs, or test testingprocedures being developed on the Ethernet®.

There will be described examples of device configuration of atransmission station for double ring network systems according to thepresent invention, before entering specific description of embodimentexamples and procedures of the embodiment 4 (claim 4) et seq.

FIG. 3 and FIG. 4 show configurations of hardware constitutingembodiments (the 1^(st)) and (the 2^(nd)) of transmission stations of adouble ring network system according to the present invention.

The configurations of hardware in FIG. 3 and FIG. 4 are different fromeach other, particularly in that the hardware configuration FIG. 3includes an INZ frame reception detecting circuit 40 (RRR-DET-A), an INZframe reception detecting circuit 39 (RRR-DET-B), and an RRR framedestination address holding circuit 38 (RRR-RCV-ADRS), which are omittedfrom an arrangement in FIG. 4, which is referred to a frame detectingsection 45 in FIG. 4 to tell it from FIG. 3.

As a communication port section 10 on one hand, a port A is configuredwith a receiver (RVR-A) and a transmitter (TVR-A) to implementbi-directional communications with an adjacent station. And, as acommunication port section 11 on the other hand, a port B is configuredwith a receiver (RVR-B) and a transmitter (TVR-B) to implementbi-directional communications with an adjacent station.

Upon a reception at the port A, as an output of the RVR-A, a receptionsignal (SIG-RV-A) from the port A is lead to a repeater A (FW-A)designated at 12, and a reception permitting switch 18 (SW-RVC-A), andinside a frame detection determiner 31, where it is lead to a receptionanomaly detecting circuit 32 (RCV-ERR-A), a SYN frame detecting circuit34 (SYN-DET-A), the RRR frame reception detecting circuit 37(RRR-DET-A), the RRR frame destination address holding circuit 38(RRR-RCV-ADRS), an INZ frame reception detecting circuit 40 (INZ-DET-A),and an INZ frame source address holding circuit 41 (INZ-TX-ADRS-A).

Likewise, upon a reception at the port B being another communicationport section 11, as an output of the RVR-B, a reception signal(SIG-RV-B) from the port B is lead to a repeater B (FW-B) designated at15, a reception permitting switch 19 (SW-RCV-B), a reception anomalydetecting circuit 33 (RCV-ERR-B), a SYN frame detecting circuit 36(SYN-DET-B), the RRR frame reception detecting circuit 39 (RRR-DET-B),the RRR frame destination address holding circuit 38 (RRR-RCV-ADRS), anINZ frame reception detecting circuit 42 (INZ-DET-B), and an INZ framesource address holding circuit 43 (INZ-TX-ADRS-B).

A transmission reception control circuit 21 (MAC/DLC), adapted tocontrol transmission and reception of transmission frames compliant withEthernet® protocol, has a transmission output, which is lead to atransmission permitting switch 16 (SW-TX-A) and a transmissionpermitting switch 17 (SW-TX-B). A transmission output signal from thetransmission reception control circuit 21 (MAC/DLC) is sent, when thetransmission permitting switch 16 (SW-TX-A) is in a permitting ON state,to the TVR-A of the port A as the communication port section 10 at onehand, and when the transmission permitting switch 17 (SW-TX-B) is in anON state, to the TVR-B of the communication port section 11 at the otherhand.

When in a switch state OFF, the switch cuts transmission output signalsof the transmission reception control circuit 21 (MAC/DLC: referredsometimes to a transmission line controller), with a result that notransmission frame is sent out from a corresponding communication port.

Upon reception of a transmission frame at the port A, it is to be leadvia an output of the repeater 12 (FW-A) and a repeat permitting switch13 (SW-FW-A), to the TVR-B of the port B. If the repeat permittingswitch 14 (SW-FW-A) is on, the transmission frame received at the port Ais repeated, and as a result, it is sent out from the port B.

If off, it is cut by the repeat permitting switch 13 (SW-FW-A), and keptfrom being repeated to send out. Likewise, upon reception of atransmission frame at the port B, it is to be lead via an output of therepeater 15 (FW-B) and a repeat permitting switch 14 (SW-FW-B), to theTVR-A of the port A.

If the repeat permitting switch 14 (SW-FW-B) is on, the transmissionframe received at the port B is repeated, and as a result, it is sentout from the communication port 10 (referred sometimes simply to a portA). If off, it is cut by the repeat permitting switch 14 (SW-FW-b), andkept from being repeated to send out.

Upon reception of a transmission frame at the port A, it is to be leadvia the reception permitting switch 18 (SW-RCV-A), to a first-comereception selecting circuit 20 (RCV-SEL).

Likewise, upon reception of a transmission frame at the port B (referredsometimes simply to a port B), it is to be lead via the receptionpermitting switch 19 (SW-RCV-B) designated at 19, to the first-comereception selecting circuit 20 (RCV-SEL). The first-come receptionselecting circuit 20 (RCV-SEL) checks for an overlap between receptionsignals from port A and port B, and if it is found, makes a selectionfor a reception to be completed with a priority to a transmission signalreceived at the first-come port side. The determination of first-comewill be described later on.

An RCV-SEL output from the first-come reception selecting circuit 20(RCV-SEL) is lead to the transmission reception control circuit 21(MAC/DLC) as a transmission line controller, where it is processed forreception. According to the present invention, a double ring networksystem is configured in a ring form, nonetheless, to be equivalent to abus type network, while working in a sound state, and at transmissionstations except for terminal stations, a transmission frame is receivedtemporarily at either port, depending on positional relations betweenown station and transmission frame sending stations.

And, at the terminal stations, being connected in a ring form wheretransmission frames to be received come up to both ports, normally at ablocked port side the reception permitting switch is turned off,allowing a reception input at an unblocked port side.

In this invention, such the reception permitting switches, transmissionpermitting switches, and repeat permitting switches are controlled toswitch on and off status thereof.

An MPU 24, which is configured as a core microprocessor, followsprocedures of programs stored in (a PROM among) program memories(employing the PROM, a working RAM memory, and a RAM), reading setvalues as necessary, and writing necessary data, temporarily holding orreading, to implement processes of, among others, Ethernet® transmissionprotocol and sequence procedures at transmission stations according tothis invention.

An IOC 22 is configured as an input output control circuit for receivingwritten data from the MPU 24 to output control signals to requiringcircuits, or for receiving status inputs of respective circuits for theMPU 24 to read.

A DP-RAM 26 is configured as a dual-port memory circuit for storage ofdata on transmission frames received or to be transmitted at theMAC/DLC, and as a host linking interface circuit 28 for an external hostdevice 29 linked with the transmission station (as a memory circuit forexchange of condition status, and control commands, as well as for datato be transmitted or received through the HOST-IF). The DP RAM 26 isaccessed from the MPU 24, HOST-IF 28, and MAC-DLC 21, and a DPRAMcontroller has reading and writing timings controlled by the DPRC 27.

The reception anomaly detecting circuit 32 (RCV-ERR-A) and the receptionanomaly detecting circuit 33 (RCV-ERR-B) are circuits for detectingreception anomalies corresponding to the port A and the port B,respectively.

The reception anomaly may be reception of preamble patterns as receptionclock synchronizing signals typical to Ethernet®, greater in number thanspecified, having dividable carrier signals of arrived frames.

To the contrary, there may be an occurrence of detection anomalydetermined by detection of consecutive reception errors greater innumber than specified, such as errors greater in number than specifiedas consecutively detected by checks to an error detection code (FCS) oftransmission frame provided for Ethernet® transmission frames, orfailures in detection of a required preamble pattern, while fordetection circuits the range excludes FCS check means provided for theDLC/MAC and a static processing of results thereof by the MPU 24.

The SYN frame detecting circuit 34 (SYN-DET-A) and the SYN framedetecting circuit 36 (SYN-DET-B) are circuit for detecting arrivals ofSYN frames corresponding to the port A and the port B, respectively.

On the other hand, the SYN absence detecting circuit 35 (NO-SYN-DET-A/B)is a circuit for detecting an occurrence of a long duration of aSYN-free silent state.

The RRR frame reception detecting circuit 37 (RRR-DET-A) and the RRRframe reception detecting circuit 39 (RRR-DET-B) are circuits fordetecting reception of RRR frames corresponding to the port A and theport B, respectively.

The RRR frame destination address holding circuit 38 (RRR-RCV-ADRS) is acircuit for taking in, to hold, a filed of destination address (DA) in areceived RRR frame. The RRR-RCV-ADRS has a circuit configuration adaptedto take in signals received at both sides.

The INZ frame reception detecting circuit 37 (INZ-DET-A) and the INZframe reception detecting circuit 38 (INZ-DET-B) are circuits fordetecting reception of INZ frames corresponding to the port A and theport B, respectively.

The INZ frame source address holding circuit 41 (INZ-TX-ADRS-A) and theINZ frame source address holding circuit 41 (INZ-TX-ADRS-B) are circuitsfor holding fields of source addresses (SA) in received INZ frames,corresponding to the port A and the port B, respectively.

An interrupt signal detecting circuit 23 (IRP) is configured as acircuit for detecting interrupt signals as signals interrupting toinform the MPU 24 of occurrences of events detected in circuitry oftransmission station.

Enumerative as interrupt signals are those o£ reception anomalyoccurrence detection (IRP-RE-A, -B), SYN absence detection (IRP-NO-SYN),SYN frame reception detection (IRP-SYN-A, -B), RRR frame receptiondetection (IRP-RRR-A, -B), INZ frame reception detection (IRP-INZ-A,-B), MAC/DLC transmission or reception completion detection (IRP-DLC),processing requests to MPU (IRP-HOST), processing requests from MPU tohost device (IRP-STN), etc.

A C-bus constitutes a common data bus connected to the MPU 24, andthrough the C-bus, the MPU 24 is adapted to read, among others, detectedstatus in particular of the NO-SYN-DET-A/B, pieces of RRR framedestination address information held in the RRR-RCV-ADRS, and pieces ofINZ frame source address information held in the INZ-TX-ADRS-A, -B.

The present invention presuppose, as the embodiment 11 (claim 11),employing a transmission frame in compliance with the ISO/IEC 8802-3Ethernet® standard.

It is noted that an ISO/IEC 8802-3 Ethernet® standard-complianttransmission frame is illustrated in FIG. 23.

In FIG. 23, designated at PRE is a preamble pattern, 7-byte length, forreception signal synchronization, SFD is a frame starting pattern,1-byte length, DA is a destination address, SA is a source address,LEN/TYPE is a type code number indicating a protocol type oftransmission frame, and Inf is an information field of transmissionframe.

The RRR frame destination holding circuit 41 (RRR-RCV-ADRS) is adaptedas a circuit for exclusively taking in, to hold, the DA field, and theINZ frame source address holding circuit 41 (INZ-TX-ADRS-A) as well asthe INZ frame source address holding circuit 43 (INZ-TX-ADRS-B), the SAfield.

For embodiment examples according to the embodiment 11 (claim 11),transmission frames employable as SYN, RRR, INZ, or INZ-COMP in thiscontrol system are not limited to any specific Ethernet® frame format.

The may well be an embodiment example of format in which those controlframes are identifiable. Practically, there is a method of takingLEN/TYPE number, whereas this requires permission of a registrationoffice administrating Ethernet® protocol Type numbers.

Further, there is a method of putting a piece of identifying informationin a field of information to be defined by a protocol Type number thathas been already given. One may implement, among others, a method ofputting a piece of identifying information in a fixed data fieldposition of a TCP data field or an extended field of a TCP headerdefined in the TCP/IP protocol that is general in the Ethernet®, oremploy an exclusive format according to the UDP protocol.

For the embodiment 4 (claim 4) through the embodiment 10 (claim 10),transmission stations described have a configuration including a repeatpermitting switch 13 (SW-FW-A), a repeat permitting switch 14 (SW-FW-B),a transmission permitting switch 16 (SW-TX-A), a transmission permittingswitch 17 (SW-TX-B), a reception permitting switch 18 (SW-REC-A), and areception permitting switch 19 (SW-REC-B), of which a respective one hasa controlled switch status according to a protocol to be implemented, asa point.

For instance, the transmission stations have an initial state asillustrated in FIG. 6, where the CPU of the computer section 30 isoperated for a setting to turn the repeat permitting switch 13 (SW-FW-A)off, the repeat permitting switch 14 (SW-FW-B) off, the transmissionpermitting switch 16 (SW-TX-A) on, the transmission permitting switch 17(SW-TX-B) on, the reception permitting switch 18 (SW-RCV-A) off, and thereception permitting switch 19 (SW-RCV-B) off; and have an MS portundefined, and a station mode undefined. In other words, thetransmission stations are set to a condition fundamentally identical tothe condition they have when powered on.

With the setting illustrated in FIG. 6, the MPU 24 of the computersection 30 makes the transmission reception control circuit 21 (MAC/DLC)output a transmission output signal to the transmission permittingswitches 16 (SW-TX-A) . . . .

By that, it is sent from the TVR-A of the communication port A to atransmission line, and through the transmission permitting switch 17(SW-TX-B), from the TVR-B of the communication port B to a transmissionline, as a frame to be transmitted.

For double ring networks and network systems making use of a controlsystem thereof according to the present invention, there is supposed aninitial condition of what is referred herein to a double ring network,as a first media portion.

FIG. 6 is an illustration of switch status and station mode of arespective station at a time of initialization start, with respect tothe embodiment 4 (claim 4), embodiment 5 (claim 5), embodiment 6 (claim6), and embodiment 7 (claim 7). It represents a condition fundamentallyidentical to that the transmission station has when powered on. Therewill be an INZ frame first received and detected at one of twocommunication ports being the port A and the port B, which will bereferred to as an MS port.

For a transmission station according to the present invention, theconfiguration is symmetric in hardware structure between a transmissionsystem and a reception system, so it is unnecessary to uniquely limitthe communication port A or the communication port B to eithercommunication port. In other words, there is no problem with the port Aor B, whichever is selected to implement the claimed procedure.

However, in the following specific examples of embodiments, for aconvenient purpose of comprehensible description with reducedcomplexity, each transmission station is assumed, in accordance withhardware configuration examples illustrated in FIG. 3 and FIG. 4, tohave on the observers' left a communication port as a port A, and on theobservers' right a communication port as a port B, which will beuniformly referred to.

As will be described later on in correspondence to respective claims,the station mode transits, as illustrated in FIG. 8, from the“undefined” status (start) identical to a status it has when powered on,through an intermediate mode “Not terminal station”, to any status ofterminal station “STT-L”, repeater station “Normal”, and terminalstation “ST-T-R”.

It is noted that in accordance with as-assumed limitation ofcorrespondence to the port A and the port B in hardware configuration oftransmission station described, the terminal station ST-T-L represents atransmission station blocked at the port B side, and the terminalstation ST-T-R represents a transmission station blocked at the port Aside, which will be uniformly referred to.

For the embodiment 4 (claim 4), FIG. 9 illustrates sequences of INZframes to be transmitted for intercommunications between transmissionstations. Those initializing sequences will be detailed later on.

In the sequence chart of FIG. 9, a master station MS transmits INZframes from transmission station #ST1 to . . . transmission station #ST4and transmission station #ST8 transmission station #ST5. Having receivedINZ frames from transmission station #ST1 to . . . transmission station#ST4 and transmission station #ST8 . . . transmission station #ST5return INZ frames to adjacent transmission stations of youngeraddresses.

With such an initialization completed, if an INZ frame sent to a certaintransmission station fails to come back from the transmission station,it is assumed that a route to the transmission station has an anomaly(disconnection).

It is noted that for an INZ frame to be returned to an adjacenttransmission station of a younger address in the description above, atransmission station that have received the INZ frame may not return theINZ frame.

Further, FIG. 10 and FIG. 11 show a flowchart describing an initializingprocess at a respective transmission station, excepting the master (MS)station, wherein it has undefined status and sends INZ frames from apair of communications ports, to determine adjacent stations and whetheror not it is a terminal station. This flowchart will be described lateron.

FIG. 12 and FIG. 13 show a flowchart including an initializing processof the MS station ST1, particularly encompassing flows of interactiveactions at transmission stations ST2 and ST8 as adjacent stations of theMS station, in accordance with the initializing process at therespective station shown in FIG. 10 and FIG. 11.

It is noted that the example of configuration of double ring networksystem illustrated in FIG. 9 is associated with the example in FIG. 1,without restrictions such as to the total number of transmissionstations, and the numbering for identification of transmission stations#ST1 to #ST9. Further, for claim 4, the embodiment examples of hardwareconfiguration shown in FIG. 3 FIG. 4 are applicable.

As a transmission station to be a base, if #ST1 is set an MS station,then as illustrated in FIG. 9 the MS station enters an initialization,starting a ST timer software-controlled by the MPU 24 as shown at a stepS0 in FIG. 12-FIG. 13.

Further, at a step S1, it implements checks of adjacent stations, whilein this case ST2 and ST8 perform checks of corresponding adjacentstations for a terminal station. Then, the MPU 24 generates by softwarecontrol initialization-instructing INZ frames periodically, each timewhen the ST timer times up, till the end of a step S3 where theinitialization becomes complete. And the MP 24 drives the transmissionreception control circuit 21 (MAC/DLC) to hold the transmissionpermitting switch 16 (SW-TX-A) and the transmission permitting switch 17(SW-TX-B) in their on states, and send INZ frames from both port A andport B.

Transmission stations have an initial state, where the switches are setas shown in FIG. 6 to a condition in which both ports are blocked, andreception-prohibited, and therefore at processing steps shown in FIG.12-FIG. 13, an arrival of INZ frame is checked for by the INZ framereception detecting circuit 40 (INZ-DET-A) or the INZ frame receptiondetecting circuit 42 (INZ-DET-B).

By that, if an INZ frame is detected at the communication port A by theINZ frame reception detecting circuit 40 (INZ-DET-A), an INZ framedetecting signal (IRP-INZ-A) is sent out. By the INZ frame receptiondetecting circuit 42 (INZ-DET-B), an INZ frame detecting signal(IRP-INZ-B) is sent out.

And, by an interrupt of the signal to be INZ frame detecting signal(IRP-INZ-A) or INZ frame detecting signal (IRP-INZ-B), the MPU 24processing it on software catches the reception of an INZ frame, andchecks which port is the reception port where it is received.

For SIG-RV-A reception signals, i.e., frames received (L-handed) at portA, there are detections and determinations to be performed, which areimplemented by the frame detecting determiner 31. For such detectionsand determinations, the frame detecting determiner 31 includes:

-   -   the reception anomaly detecting circuit 32 (RCV-ERR-A) adapted,        when it has detected anomaly in reception of SIG-RV-A, to output        an IRP-RE-A signal (referred sometimes to a reception signal A        anomaly detecting signal) to the computer section 30.

The SYN frame detecting circuit 34 (SYN-DET-A) is adapted, as theSIG-RV-A reception signal from the communication port 10 is a SYN frame,to output an IRP-SYN-A signal (referred sometimes to a SYN framedetecting signal A) to the computer section 30 and the SYN absencedetecting circuit 35 (NO-SYN-DET-A/B).

The RRR frame detecting circuit 37 (RRR-DET-A) is adapted, when it hasdetected an SIG-RV-A reception signal from TVR-A of the communicationport 10 (port A) as an RRR frame, to output an IRP-RRR-A signal (an RRRframe reception detecting signal A) to the computer section 30.

The INZ frame detecting circuit 40 (INZ-DET-A) is adapted, when it hasdetected an INZ frame of an SIG-RV-A signal received at thecommunication port 10 (communication port A), to output an IRP-INZ-Asignal (an INZ frame reception detecting signal A) to the computersection 30.

The INZ frame source address holding circuit 41 (INZ-TX-ADRS-A) isadapted to hold a source address (SA) field of an INZ frame in anSIG-RV-A signal received at the port A.

Further, the reception anomaly detecting circuit 33 (RCV-ERR-B) isadapted, when it has detected anomaly in reception of SIG-RV-B from thecommunication port 11 (port B), to output an IRP-RE-B signal (referredto a reception signal anomaly detecting signal) to the computer section30.

The SYN frame detecting circuit 36 (SYN-DET-B) is adapted, as theSIG-RV-B reception signal from the communication port 11 is a SYN frame,to output an IRP-SYN-B signal (referred sometimes to a SYN framedetecting signal B) to the computer section 30 and the SYN absencedetecting circuit 35 (NO-SYN-DET-A/B).

On the other hand, the SYN absence detecting circuit 35 (NO-SYN-DET-AB)is adapted to output an IRP-NO-SYN signal (a SYN absence detectingsignal) to the computer section 30, if it has not received any IRP-SYN-Asignal (SYN frame reception detecting signal A) from the SYN framedetecting circuit 34 (SYN-DET-A) or any IRP-SYN-B signal (SYN framereception detecting signal B) from the SYN frame detecting circuit 36(SYN-DET-B).

The RRR frame detecting circuit 39 (RRR-DET-B) is adapted to detect anRRR frame in an SIG-RV-B from RVR-B of the communication port 11 (portB), and upon a detection, to output an IRP-RRR-B signal (an RRR framereception detecting signal B) to the computer section 30.

The RRR frame destination address holding circuit 38 (RRR-RCV-ADRS) isadapted for taking in, to hold, a destination address (DA) field of anRRR frame in an SIG-RV-B signal received at the communication port 11(port B).

The RRR destination address holding circuit 38 (RRR-RCV-ADRS) is adaptedfor taking in reception signals at both sides in time to take in thedestination address fields.

The INZ frame source address holding circuit 43 (INZ-TX-ADRS-B) isadapted to hold a source address (SA) field of an INZ frame in anSIG-RV-B as a reception signal received at the port B.

More specifically, there are initialization-instructing INZ frames sentin both directions (communication ports A and B), followed by waits forarrivals of INZ frames (responding acknowledgement frames (INZ-COMP))from adjacent stations (refer to FIG. 12).

For the INZ frames to be sent, the computer section 30 employs thetransmission reception control circuit 21 (MAC/DLC) for setting up, asshown in FIG. 6, blocked states and reception-prohibited states (withthe SW-TX-A and the SW-TX-B turned on) for the transmission in bothdirections.

And, if an arrival of an INZ frame is detected by the INZ framereception detecting circuit 42 (INZ-DET-B) or the INZ frame receptiondetecting circuit 40 (INZ-DET-A) with respect to a reception signal,SIG-RV-B at the communication port B, or that at the communication portA or A, then the computer section 30 turns on the reception permittingswitch 19 (SW-RCV-B) or the reception permitting switch 18 (SW-RCV-A),to take it in.

The first-come reception selecting circuit 20 (RCV-SEL) checks thereception permitting switch 18 (SW-RCV-A) and the reception permittingswitch 19 (SW-RCV-B), determining which is the communication port wherethe reception has occurred, and informs the transmission receptioncontrol circuit 21 (MAC/DLC) of the result. A reception port that hasfirst received is set as an MS port.

By this, that port which has received a first INZ frame forinitialization is set as the MS port.

Next, at a step S01 or S02 in FIG. 12-FIG. 13, if an INZ frame from themaster station MS is received by an adjacent station (#ST2 or #ST8),then the blocked state from that reception port to the othercommunication port is changed to an unblocked state, by turning on therepeat permitting switch 13 (SW-FW-A) or the repeat permitting switch 14(SW-FW-B), whichever corresponds thereto.

Likewise, the reception permitting switch 18 (SW-RCV-A) or the receptionpermitting switch 19 (SW-RCV-B), whichever corresponds to that receptionport, is turned on, thereby permitting transmission frames receivedthereafter at the reception port to be taken in.

Further, the adjacent station has the transmission permitting switch 16(SW-TX-A) or the transmission permitting switch 17 (SW-TX-B), whichevercorresponds to that reception port, held on temporarily alone, to sendan INZ frame as a responding acknowledgment from the reception port, andhas a station mode “not terminal”. After that, at an S11, it receivesand detects a subsequent INZ frame from the master station, when itstarts the ST timer, waiting for an event of step S2.

Next, still at the S11 following S01 or S02 having sent an INZ frame tothe master station, it checks for an arrival of a subsequent INZ frame,and under this condition, it enters a step S21 or S23, where if itreceives and detects an INZ frame as a responding acknowledgment sentfrom an adjacent station on the opposite side to the MS port side, thenthe blocked state from that reception port to the other communicationport is changed to an unblocked state, permitting incoming transmissionframes to be received and taken in. As a result, this station isoperative as a repeater station permitting transmission frames to bereceived at communication ports on both sides, and received signals tobe taken in and repeated to the opposite sides, and has a station mode“normal”. In the example illustrated in FIG. 9, ST2, ST3, and ST4 aswell as ST8 and ST7 are set to the normal mode.

On the other hand, at steps S11 and S12 in FIG. 12-FIG. 13, if themaster station MS receives INZ frames as responding acknowledgments fromadjacent stations ST2 and ST8, then it has a normal mode. The INZ-DET-Aand -B are configured as means for an ensured detection of INZ's asresponding acknowledgements simultaneously arriving at from bothdirections.

This system is adapted to have an increasing number of normal stationsincremented one by one in both directions from the MS station, so thereappear transmission stations receiving INZ frames sent from the MSstation, at communications ports on both sides, simultaneously or with atime lag, as they are determined in dependence on a total number oftransmission stations constituting the ring form network and a totallength of transmission line connecting the transmission stations witheach other.

At a step S03 or S04 in FIG. 10, under a condition that an MS port isestablished, if an INZ frame is received at a blocked port, then aterminal station ST-T-R as well as ST-T-L is temporarily determined independence on that reception port. For instance, if #ST5 has received anINZ left-handed after a reception at a port A where it received an INZframe from the master (MS), then #ST5 stands as an ST-T-R.

For a transmission station (#ST6, for instance) to be another terminalstation as it has been kept from sending an INZ frame as a respondingacknowledgment from a reception port at the step S03 or S04, there is astep S24 corresponding to the S03 or S22 corresponding to the S04, whereif it fails to receive, within a prescribed interval of time for the STtimer to time up, an INZ frame as a responding acknowledge from theother terminal station that has been already established, then it has aterminal mode ST-T-L or ST-T-R as an opposing terminal station. For theST-T-L, refer to description of FIG. 29.

Further it is noted that although FIG. 9 illustrates a case in which ST5and ST6 stand as terminal stations as a result of the above-noted normalprocedure, if it is failed at the step S22 or S24 in FIG. 11 to receivean INZ frame as a responding acknowledgment from an adjacent station atan expected reception port side, the terminal station ST-T-L or ST-T-Ris determined at that point of time in accordance with the expectedreception port side.

Likewise, for the MS station also, there is a step S13 or S14 in FIG. 12to have a station mode determined as ST-T-R or ST-T-L, for an anomalyfound in functions for communications including transmission routes downto adjacent stations, adjacent station communication functions, andtransmission routes from adjacent stations to own station.

It is noted that step numbers of procedures for #ST2 and #ST8 in FIG.12-FIG. 13 correspond to step numbers in FIG. 10-FIG. 11.

By the foregoing, it is possible to implement an initialization so thattransmission frames sent from transmission stations constituting adouble ring network system are kept from circulating in the networkconfigured in a ring form.

It is noted that FIG. 5 illustrates switch status for ST-T-L and ST-T-Rset as terminal stations in initialization. And, FIG. 7 additionallyillustrates switch status at normal stations.

That is, for a ST-TL-L to be set, the computer section 30 turns therepeat permitting switch 13 (SW-FW-A) on, the repeat permitting switch14 (SW-FW-B) off, the transmission permitting switch 16 (SW-TX-A) on,the transmission permitting switch 17 (SW-TX-B) off, the receptionpermitting switch 18 (SW-RCV-A) on, and the reception permitting switch19 (SW-RCV-B) off. Accordingly, if disconnection occurs between ST-T-Land ST-T-R, reception signals are taken in at the port A, and frames arereturned simply at the port A.

Further, for a ST-T-R to be set, the computer section 30 turns therepeat permitting switch 13 (SW-FW-A) off, the repeat permitting switch14 (SW-FW-B) on, the transmission permitting switch 16 (SW-TX-A) on, thetransmission permitting switch 17 (SW-TX-B) on, the reception permittingswitch 18 (SW-RCV-A) off; and the reception permitting switch 19(SW-RCV-B) on.

Accordingly, reception signals are taken in at the port B, and framesare returned simply at the port B.

With respect to the embodiment 5 (claim 5), FIG. 14 illustratessequences of INZ frames to be transmitted between transmission stations,which will be described. There is an initializing process to beimplemented at respective stations excepting a master (MS) station,which is illustrated in FIG. 15-FIG. 16.

Shown in FIG. 17-FIG. 18 is a flowchart involving an initializingprocess for the MS station ST1. Further, it specifically involvesactions in processes for intercommunications at transmission stationsST2 and ST8 as adjacent stations of the MS station, as they comply withprotocols for the initializing process at respective transmissionstations illustrated in FIG. 14.

It is noted that the example of configuration of double ring networksystem illustrated in FIG. 14 is fit to the example of FIG. 1, withoutrestrictions to, among others, the total number of transmissionstations, and the numbering for identification of transmission stations#ST1 to #ST9.

Further, for the embodiment 5 (claim 5), hardware configurations of theembodiment examples illustrated in FIG. 3 and FIG. 4 are adaptive.

As a transmission station to be a base, if #ST1 is set as an MS station,then the MS station sends initialization instructing INZ frames in bothdirections, starting an ST timer, as illustrated in FIG. 14 and as shownat a step S0 in FIG. 17-FIG. 18. And, at a step S1 in FIG. 17, it waitsfor INZ frames (INZ-COMP) as responding acknowledgements as responsesfrom adjacent stations, #ST2 and #ST8 in this case.

Respective transmission stations have a switch status in an initialphase, where both ports are blocked and reception-prohibited, asillustrated in FIG. 6, and #ST2 and #ST8 go to a step S01 or S03 shownin FIG. 17-FIG. 18, where the INZ frame reception detecting circuit 40(INZ-DET-A) or the INZ frame reception detecting circuit 42 (INZ-DET-B)detects an arrival of INZ frame.

And, by an interruption of an INZ frame reception detecting signal(IRP-INZ-A) or an INZ frame reception detecting signal (IRP-INZ-B), asit is followed by software processes at the MPU 24, a reception of INZframe is confirmed, and a reception port to be either port where thereception has occurred is confirmed (refer to S11 to S15 in FIG. 17).

That is, it is determined whether or not the INZ frame receptiondetecting circuit 40 (INZ-DET-A) has output an INZ frame receptiondetecting signal (IRP-INZ-A) or whether or not the INZ frame receptiondetecting circuit 42 (INZ-DET-B) has output an INZ frame receptiondetecting signal (IRP-INZ-B). If any INZ frame reception detectingsignal (IRP-INZ-A) is output, then the transmission permitting switch 17(SW-TX-A) and the reception permitting switch 19 (SW-TX-A) are turnedon. If any IRP-INZ-B is output, then the SW-TX-B and the SW-RCV-B areturned on.

The first-come reception selecting circuit 20 (RCV-SEL) determines whichcommunication port has first received a signal, and outputs a result ofthis determination to the transmission reception control circuit 21(MAC/DLC).

By doing so, that port which has received a first INZ frame in theinitialization is set as an MS port.

Upon reception of an INZ frame from the master MS station at a step S01or S03 in FIG. 15-FIG. 16, the MPU 24 changes the blocked state fromthat reception port (MS port) to the other communication port to anunblocked state, by turning on the repeat permitting switch 13 (SW-FW-A)or the repeat permitting switch 14 (SW-FW-B), whichever corresponds tothe MS port.

Likewise, the reception permitting switch 18 (SW-RCV-A) or the receptionpermitting switch 19 (SW-RCV-B), whichever corresponds to the MS port,is turned on, thereby permitting transmission frames received thereafterat the reception port to be taken in.

Further, source address information in the received and detected INZframe is read from the INZ frame source address holding circuit 41(INZ-TX-ADRS-A) or the INZ frame source address holding circuit 42(INZ-TX-ADRS-B), whichever corresponds to the reception port, and heldas an adjacent station address on the MS port side. Further, the stationhas a station mode “not terminal station”.

Still further, at a step S11 or S12, whichever corresponds to the MSport, it sends acknowledging INZ frames in which adjacent stationaddresses held in advance are set as destinations, from both ports,permitting a transmission frame to be received and taken in at a port onthe opposite side to the MS port, and starts the ST timer, waiting foran event of step S2.

If the S11 or S12 having sent an INZ frame in which an address of anadjacent station on the MS port side is set as a destination is followedby an INZ frame as a responding acknowledgment sent from an adjacentstation on the opposite side to the MS port side, addressing ownstation, and received and detected at a step S21 or S22, then theblocked state from that reception port to the other communication portis changed to an unblocked state, permitting incoming transmissionframes to be received and taken in.

As a result, this transmission station has a station mode “normal”, as arepeater station permitting transmission frames to be received and takenin at communication ports on both sides, and repeated to the othersides.

In the example illustrated in FIG. 14, ST2, ST3, and ST4 as well as ST8and ST7 are set to a normal mode.

On the other hand, at steps S11 and S12 in FIG. 12-FIG. 13, if themaster station MS receives INZ frames as responding acknowledgments fromadjacent stations ST2 and ST8, then it has a normal mode. The INZ framereception detecting circuit 40 (INZ-DET-A) and the INZ frame receptiondetecting circuit 42 (INZ-DET-B) are configured as means for an ensureddetection of INZ's as responding acknowledgements simultaneouslyarriving at from both directions.

This system is adapted to have an increasing number of normal stationsincremented one by one in both directions from the MS station, so thereappear transmission stations receiving INZ frames sent from the MSstation, at communications ports on both sides, simultaneously or with atime lag, as they are determined in dependence on a total number oftransmission stations constituting the ring form network and a totallength of transmission line connecting the transmission stations witheach other.

At a step S02 or S04 in FIG. 15-FIG. 16, under a condition that an MSport is established, if an INZ frame is received at a port on theopposite side, then a terminal station ST-T-L or ST-T-R is determined independence on the MS port.

Further, the station having been set as a terminal goes to a step S11 orS12, where it sends an INZ frame as a responding acknowledgmentaddressing an adjacent station on the MS port side. On the other hand,in opposition to a transmission station A determined as an ST-T-L orST-T-R, there is a transmission station B as a terminal station on theother side, which is to receive and detect an INZ frame not addressingown station as a destination, before the ST timer times up, in theprocess of waiting an INZ frame as a responding acknowledgmentaddressing own station that the transmission station A is expected tosend in response to an INZ frame the transmission station B has sent.

If it has received and detected at a reception port opposing an MS portan INZ frame not addressing own station as a destination, it goes to astep S23 or S24, where it stands as a terminal station ST-T-L or ST-T-Ropposing the transmission station A.

Further it is noted that although FIG. 14 illustrates a case in whichST5 and ST6 stand as terminal stations as a result of the above-notednormal procedure, if it is failed at the step S25 or S26 in FIG. 15-FIG.16 to receive an INZ frame as a responding acknowledgment addressing ownstation as a destination from an adjacent station at an expectedreception port side, the terminal station ST-T-L or ST-T-R is determinedat that point of time in accordance with the expected reception portside.

Likewise, for the MS station also, there is a step S13 or S14 in FIG. 12to have a station mode determined as ST-T-R or ST-T-L, for an anomalyfound in functions for communications including transmission routes downto adjacent stations, adjacent station communication functions, andtransmission routes from adjacent stations to own station.

It is noted that step numbers of procedures for #ST2 and #ST8 in FIG.17-FIG. 18 correspond to step numbers in FIG. 15-FIG. 16. By theforegoing, it is possible to implement an initialization so thattransmission frames sent from transmission stations constituting adouble ring network system are kept from circulating in the networkconfigured in a ring form.

Further, FIG. 5 illustrates switch status for ST-T-L and ST-T-R set asterminal stations in initialization as described. And, FIG. 7additionally illustrates switch status at normal stations.

With respect to the embodiment 6 (claim 6), FIG. 14 illustratessequences of INZ frames to be transmitted, FIG. 15 and FIG. 16 show aninitialization process for transmission stations excepting an MSstation, and FIG. 17 and FIG. 18 show that of the MS station. Further,FIG. 3 and FIG. 4 illustrate examples of configuration of transmissionstations.

Transmission frames include a destination address representing adestination, and a source address representing a source. FIG. 23illustrates a transmission frame compliant with ISO/IEC8802-3 Ethernet®,where they correspond to DA and SA as field information at specifiedlocations in the transmission frame.

In embodiment example corresponding to the embodiment 5 (claim 5), arespective transmission station excepting the MS station is adapted,when it has first received an INZ frame in the initializing period, toset the reception port as an MS port, take out a source address (DA) inthe received INZ frame, and hold it as an address of an adjacenttransmission station on the MS port side.

Further, in a row, it sends in both directions INZ frames as aresponding acknowledgment addressing as a destination the held addressof the adjacent station on the MS port side. Although the adjacentstation on the MS port side is to receive an INZ frame addressing ownstation as a destination at a port on the opposite side to an MS port,its source address is an address of a transmission station subsequent toown station in view from the MS station, i.e., adjacent to the port onthe opposite side to the MS port.

For a respective transmission station excepting the master station MS,it is possible to acquire and hold pieces of address information oftransmission stations adjacent on an MS port side or to a port on theopposite side, at steps S11 and S12 for the master station MS in FIG.17, or in the process of transition to a normal mode by a sequence ofsteps including step S01 or S03 and S11 or S12 in FIG. 15-FIG. 16 andS21 or S22 in FIG. 18, in the process of transition to an ST-T-L orST-T-R mode by steps including step S02 or S04 and S11 or S12 and S23 orS24 (refer to FIG. 17 and FIG. 18).

Further, in this initializing method, in the process of incorporatingtransmission stations one by one from a master station MS into a ringnetwork system, if, at a respective transmission station, soundness of areception system on the MS port side, a transmission line to an adjacentstation on the opposite side to the MS port, functions for transmissionand reception at the adjacent station, and a transmission line returningfrom the adjacent station to own station and an associated receptionsystem of own station are free of anomalies, it necessarily receives anddetects an INZ frame as a responding acknowledgment from the adjacentstation, whereby the mutually adjacent stations can act together toensure the soundness of a bi-directional communication line in between,permitting acquisition and storage of addresses of transmission stationsadjacent on the MS port side or to a port on the opposite side.

With respect to the embodiment 7 (claim 7), it is possible for arespective terminal station to inform an MS station and transmissionstations of a completion of the initialization of double ring network,by sending an INZ-COMP frame as an indication of initializationcompletion containing a terminal station address and terminal stationmode, at the time when two mutually adjacent terminal stations ST-T-Land ST-T-R are configured at positions determined in dependence on atotal number of transmission stations constituting a network system of aring form, and a total length of a transmission line connecting thetransmission stations with each other, or at the time when adetermination to stand as a terminal station is made on the way ofinitialization by absence of reception of an INZ frame as a respondingacknowledgment from a station adjacent to own station, in examples ofinitialization described with respect to the embodiment 4 (claim 4) orthe embodiment 5 (claim 5), that is, after determination of ST-T-L andST-T-R at step S03 or S04, or S22 or S24 in Fig.-FIG. 11 in theinitializing method according to the embodiment 4 (claim 4), or at stepS02 or S04, S23 or S24, or S25 or S26 in FIG. 15-FIG. 16 in theinitializing method according to the embodiment 5 (claim 5).

At a respective transmission station where the initialization iscompleted, transmission frames can be sent, received and taken in atboth ports, as software control of the MPU permits INZ-COMP frames to begenerated and transmission-controlled by MAC/DLC to send from bothports, as well as incoming and received INZ-COMP frames to bereception-controlled by MAC/DLC to take in, for detection,determination, and processing by software control of the MPU.

However, as the completion of initialization provides a functionalconfiguration of bus-type network, if both terminal stationssubstantially simultaneously send INZ-COMP frames, then a respectivetransmission station may have an opportunity of overlap in reception.

In that case, the first-come reception selecting circuit 50 (RCV-SEL)permits one INZ-COMP frame that has first come to bereception-controlled by MAC/DLC, to take in.

To this point, as an embodiment example of an initializing methodaccording to the embodiment 4 (claim 4), there are steps S3 and S4 shownin FIG. 10-FIG. 11, as a transmission procedure of INZ-COMP framesaddressing an MS station.

That is, a responding acknowledgement sequence with the MS stationpermits an ensured reception of INZ-COMP frame at the MS station. Thisis an embodiment example in which a resending process is continued tillreception of an INZ-COMP frame as a responding acknowledgment addressingown station as a destination, and a waiting period for resending is setto be mutually different as ST1 and ST2 in accordance with station modesST-T-L and STT-R, to avoid consecutive overlaps of INZ-COMP frames atthe MS station.

At the step S3 in FIG. 12-FIG. 13, it is allowed at the MS station sideto detect a completion of initialization, and stop sending periodicalINZ frames.

Further, as an embodiment example of an initializing method according tothe embodiment 5 (claim 5), there are steps S3 and S4 shown in FIG.15-FIG. 16, as a transmission procedure of INZ-COMP frames addressing abroadcast address as the destination.

If the master station MS receives an INZ-COMP frame addressing abroadcast address, then it sends an INZ-COMP frame as a respondingacknowledgment to an address of the source, allowing for an ensuredreception of INZ-COMP frame at the master station MS by a respondingacknowledgment sequence with the master MS.

This is an embodiment example in which a resending process is continuedtill reception of an INZ-COMP frame as a responding acknowledgment fromthe master station MS addressing a terminal station as a destination,and a waiting period for resending is set to be mutually different asST1 and ST2 in accordance with station modes ST-T-L and ST-T-R, to avoidconsecutive overlaps of INZ-COMP frames at the MS station.

At the step S3 in FIG. 17-FIG. 18, it is allowed at the MS station sideto detect a completion of initialization. It is noted that INZ-COMP's tobe sent from terminal stations may address a broadcast address as thedestination, so that whole transmission stations can detect a completionof initialization.

With respect to the embodiment 8 (claim 8), FIG. 3 and FIG. 4 illustrateexamples of configuration of transmission stations. FIG. 19 illustratesa situation of a double ring network system configured with #ST5 and#ST6 as opposing terminal stations, in which during a normal service, ananomaly has occurred in communication lines interconnecting #ST10 and#ST9.

There are no restrictions to, among others, the number of transmissionstations or locations of occurrence, or relation with positions ofterminal stations or synchronizing station.

FIG. 20 illustrates status of switches at respective transmissionstations after occurrence of transmission anomaly in communication linesinterconnecting #ST10 and #ST9.

Under a condition that the initialization is completed, a double ringnetwork system in a typical situation where it has thereon one or moretransmission stations sending one or more transmission frames, enterssuch a situation that a SYN frame containing specific informationmeeting a preset condition, whereby its arrival can be discriminated, isperiodically sent from any transmission station (synchronizing station),where an arrival of SYN frame is discriminated and detected by the SYNframe detecting circuit 34 (SYN-DET-A) or the SYN frame detectingcircuit 36 (SYN-DET-B), and output as an IRP-SYN-A or -B.

Further, absence of SYN frame reception over a preset period isdiscriminated and detected at the SYN absence detecting circuit 35(NO-SYN-DET-A/B) for each communication port, from a failed periodiccontinuation of SYN frame reception detecting signal (IRP-SYN-A) or SYNframe reception detecting signal (IRP-SYN-B).

Accordingly, the SYN absence detecting circuit 35 (NO-SYN-DET-A/B) isadapted, under a condition that a periodic arrival of SYN frame iscontinued in succession through one communication port, to detect alsothat, through the other communication port, no continued periodicarrival is found over a preset period, from IRP-SYN-A and -B signals, sothe MPU can read through the C-bus which communication port is absent ofperiodic succession of SYN frame, at the time of status change interruptof IRP-NO-SYN as a SYN-absent state detecting output signal. Further,transmission frames received through communication ports A, -B arechecked for anomaly of received signal status by the reception anomalydetecting circuit 32 (RCV-ERR-A) and the reception anomaly detectingcircuit 33 (RCV-ERR-B), in accordance with criteria for received signalstatus to be monitored and anomaly to be determined.

Next, in response to the SYN absence detecting circuit 35(NO-SYN-DET-A/B) and IRP-NO-SYN interrupt signal, the MPU 24 operates bysoftware control of the MPU 24 to change, from ON to OFF, the status ofa repeat permitting switch SW-FW-A, or -B that corresponds to thecommunication port where SYN absence is detected, to provide aninter-port repeat-prohibiting blocked state, so as not to send anytransmission frame from the other communication port through a repeatfrom the communication port where SYN absence is detected to the othercommunication port, while at the SYN-absent port A or port B, amongother transmission frames received through each communication port, theabove-noted INZ frame as well as a later-described RRR frame thatcorresponds to the configuration of transmission station in FIG. 3 isdiscriminated for detection and responded.

Further, as to reception and take-in of a transmission frame at the portwhere SYN absence is detected, a reception-prohibited state isestablished by changing status of the reception permitting switch 18(SW-REC-A) or the reception permitting switch 19 (SW-REC-A) -B,whichever corresponds thereto, from on to off. At the communication portwhere reception anomaly is detected by REC-ERR-B), the repeat permittingswitch 13 (SW-FW-A) or the repeat permitting switch 14 (SW-FW-B),whichever likewise corresponds thereto, is controlled to set a blockedstate. Further, SW-REC-A, or -B is controlled to set areception-prohibited state. Control signals from the MPU 24 torespective switches are output through the IOC.

By the above, through the way from detection of a failure occurrence toa recovery of network function by a recovery procedure, communicationports of transmission stations can be held unblocked, permitting thetransmission stations to fulfill functions of terminal stations.

With respect to the embodiment 9 (claim 9), FIG. 3 is an example ofconfiguration of transmission station. FIG. 21 shows a correspondingprocedure for recovery from a detection of failure occurrence. FIG. 19is a double ring network configured with #ST5 and #ST6 as opposingterminal stations. And, a transmission line between #ST5 and #ST6 isrecovered, and #ST5 and #ST6 are normally working in normal modes, whena transmission anomaly has occurred in communication lineinterconnecting #ST10 and #ST9, of which the situation is illustrated.There are no restrictions to, among others, the number of transmissionstations or location of occurrence, or relation with positions ofterminal stations or synchronizing station. FIG. 20 illustrates statusof switches at respective transmission stations after occurrence oftransmission anomaly in communication line interconnecting #ST10 and#ST9. FIG. 21 is a flowchart describing actions of transmission stationsin a double ring network system according to the embodiment 5.

This FIG. 21 is an example of reconfiguration from a one-point failureof the double ring network system.

For the configuration of transmission station in the example of FIG. 3,if any transmission anomaly occurs in communication line interconnecting#ST10 and #ST9, the reception via #ST9, #ST8, and #ST7 is made at theend of a communication port B of #ST6.

At #ST6, an arrival of RRR frame is discriminated for detection by theRRR-DET-A, or -B, and output as an IRP-RRR-A, or -B. Upon reception ofan RRR frame, #ST6 has destination address information in the RRR frameheld in the RRR-RCV-ADRS, so at the time status change interrupt ofIRP-RRR-A, or -B, the MPU can read it via the C-bus, and determine toprocess, including which communication port has received.

Own station address information being information for identification ofown station is set in advance in the PROM, or such as by a setting byswitches, and address information of transmission stations adjacent atthe port-A and -B sides is set to hold as adjacent station addressinformation in the RAM in or before, among others, the initializationprocedure according to the above-noted embodiment 6 (claim 6), or theprocedure for recover from failure in the instant system. Further, theMPU is adapted to read them, compare destination address information ina received RRR frame with own station address information, and determineto process by software control of the MPU, a match or mismatch.

That is, it determines a match of address, and changes a reception portof the RRR frame (referred herein sometimes to an RRR reception port) toan unblocked state, or it determines a mismatch of address, and readsaddress information of an adjacent station (#ST7 or #ST5 in thisembodiment) corresponding to the RRR reception port, generates an RRRframe addressing it as the destination, and at the timing of receptioncompletion of RRR frame, promptly send it through the RRR reception portto #ST7 or #ST5.

Further, the MPU 24 of #ST6, having sent the RRR frame, starts an STtimer configured by the above-noted software control, followed such asby a process of monitoring to detect reception of an RRR frameaddressing own station as the destination, within a prescribed period oftime, which can be determined and processed by software control of theMPU. On the other hand, if #ST10 detects an anomaly of a receptionsignal received at the communication port A side by the RRR framereception detecting circuit 37 (RRR-DET-A) or the like, then it controlswitches to a status of #ST10 O-R-M1 mode in FIG. 20. That is, #ST10stands as a terminal station ST-T-R.

Further, if #ST5 detects a SYN absence detection from the side ofcommunication port B (the port on the #ST6 side) and receives from the#ST6 side an RRR frame addressing own station, then it changes from aterminal station to a repeater station mode.

That is, its switch status is changed from a switch status (a) in FIG.20, by turning on SW-FW-B and SW-RCV-B as well as SW-FW-A and SW-RCV-A.

Accordingly, if #ST1 is a synchronizing station, #ST5 and #ST6 stand asrepeater stations, and #ST10 and #ST9 automatically stand as terminalstations, instead.

Therefore, workers can repair a transmission line between #ST10 and#ST9, without shutting down the double ring network system.

The double ring network system has thereon, in addition to SYN framesfrom a synchronizing station, among others, periodically senttransmission frames and sporadically sent transmission frames fromrespective transmission stations, as they are sent in accordance with atransmission line control system for avoiding collisions betweentransmission frames on a double ring network system as a higher layer ofOSI that is not specifically needed to prescribe for the presentinvention, and under this condition, if transmission anomaly happens incommunication line interconnecting #ST10 and #ST9 as illustrated in FIG.19, then as described with respect to the embodiment 8 (claim 8), SYNabsence will not be detected at #ST10, respective stations #ST2, #ST3,and #ST4 on a route from #ST1 being a synchronizing station to aterminal station #ST5, and #ST5, as they are still able to detectarrival and reception of periodic and consecutive SYN frames from thesynchronizing station.

On the other hand, at #ST9, #ST8, #S17, and #ST6 on a route between #ST9and a terminal station #ST6, both inclusive, there is a detection of SYNabsence, and a detection of reception anomaly as circumstances permit.Further, at #ST10, detecting periodical arrival and reception of SYNframe, there is a resultant detection of reception anomaly under theabove-noted condition.

For the example of FIG. 19, in the situation that transmission anomalyhas occurred in communication line interconnecting #ST10 and #ST9,respective stations have their switch status shown in FIG. 20. At #ST9,#ST8, and #ST7 (refer to FIG. 20( c)) as well as #ST6, thus SW-FW-B isturned off, and SW-REC-B is turned off, whereby #ST9, #ST8, and #ST7 aswell as #ST6 are each blocked and reception-prohibited at the side ofport B. At #ST10 (refer to FIG. 20 (d)), SW-FW-A and SW-REC-A are turnedoff, whereby it stands as a terminal station ST-T-R blocked andreception-prohibited at the side of port A.

As shown in FIG. 21,

between the two terminal stations, the terminal station #ST6 that has asubsequent position in a route from the synchronizing station #ST1 tothe location of anomaly goes to a step S-R0 in FIG. 21, where its switchstatus of ST-T-R: T-R-M0 mode illustrated in FIG. 7 is changed to aswitch status of terminal station #ST6 (T-R-M1) illustrated in FIG. 20,where in addition to the side of port A that has been blocked sincebefore and reception-prohibited, also the side of port B has the samestate.

Further, #ST6, where by the SYN absence detecting circuit 35(NO-SYN-DET-AB) and IRP-SYN-A, -B it is determined that anomaly hasoccurred at the side of port B, i.e., on the route to the synchronizingstation, goes as a SYN absence detecting terminal station to a stepS-R1, where it promptly reads address information of #ST5 as an opposingterminal station ST-T-L from within a RAM where it is held, and sendsRRR frames addressing it as the destination (ST5) in both directionsthrough the port -A, -B, and the ST6 starts an ST timer having aprescribed timer period set thereto, and waits for an arrival andreception of an RRR frame as a responding acknowledgment from anadjacent station, #ST7 in this case, at the side of port B on the way tothe synchronizing station.

At #ST5 being an opposing terminal station ST-T-L as the destination towhich RRR transmission frames are addressed, if it receives an RRR framesent from #ST6 addressing own station, then it goes to a step S-L1,where its condition is changed from that as a terminal station, where ithas been blocked at the side of port B, to a repeater station normalmode, where SW-FW-B is turned on and SW-REC-B is turned on, so the sideof port B is unblocked and reception-enabled.

On the way from SYN absence detecting terminal station #ST6 to locationof anomaly occurrence, respective normally operating transmissionstations #ST7, #ST8, and #ST9 have their repeat functions maintained inthat direction, and at a step S1, receive RRR frames from SYN absencedetecting terminal station #ST6 substantially at a time, with delays dueto transmission line.

At the step S21 in FIG. 21, the transmission stations each respectivelydetect an arrival and reception of an RRR frame by RRR-DET-A, and if itis determined that the destination is not own station, read an addressof an adjacent station on the way to SYN absence detecting terminalstation from within a RAM where it is held, and generate an RRR frameaddressing it as the destination. And, they each send it promptly aftercompletion of RRR frame reception, through the port A as an RRRreception port, temporarily turning SW-TX-B off, under transmissionreception control of MAC/DLC.

At a step S-R2, SYN absence detecting terminal station #ST6 that hassent RRR frames addressing ST-T-L terminal station as the destination,receives from adjacent station #ST7 on the way to the synchronizingstation, and detects an RRR frame addressing own station, within a timeinterval till the ST timer times up.

Then, after a wait till the ST timer times up, it turns the port B atthe side toward the synchronizing station that has been blocked eversince anomaly detection, and the port A opposing ST-T-L that has beenblocked since before, unblocked, and both ports, reception-enabled, tochange from its condition as a terminal station to a repeater stationnormal mode.

On the way from SYN absence detecting terminal station #ST6 to locationof anomaly occurrence, normally operating transmission stations #ST7,#ST8, and #ST9 each respectively identify at a step S21, after havingsent an RRR frame addressing an adjacent station on an RRR receptionport side as the destination from the RRR reception port side at thestep S1 in FIG. 21, but before an ST timer that has been started withthis sending times up, reception of an RRR frame addressing own stationfrom an adjacent station on the way to the synchronizing station. Then,after a wait till the ST timer times up, they each turn the port B thathas been blocked since anomaly detection, unblocked, to return to arepeater station normal mode.

On the other hand, at a step S22, for #S9 as a transmission stationadjacent the location of anomaly on the way to SYN absence detectingterminal station #ST6, it is failing to receive an RRR frame addressingown station from #ST10 even after the ST timer times up, then the port Bis kept blocked.

Accordingly, it stands as a new terminal station ST-T-L. Likewise, foroccurrence of anomaly at a location adjacent to a SYN absence detectingterminal station, if this is failing to receive an RRR frame addressingown station even after a ST timer times up with lapse of a prescribedtime, then at a step S-R2, that block which has been blocked ever sinceanomaly detection is kept blocked.

Further, the other communication port that has been blocked as aterminal station since before is unblocked, so it changes from theterminal station St-T-R to an ST-T-L.

By the foregoing, for occurrence of a transmission anomaly condition dueto one-point failure on a double ring network system, positions ofterminal stations are changed to a combination of an adjacent station onthe way from a location of anomaly occurrence to a synchronizing stationand an adjacent station on the way from the location of anomalyoccurrence to the opposite side, to thereby avoid a total shutdown ofthe network.

Further, terminal stations are re-locatable with a confirmed soundnessof bi-directional communications with adjacent stations, allowing for asubstantially simultaneous single-time completion between transmissionstations on a route to transmission stations to be new terminalstations, permitting the recovery time from anomalous state to recoveryto be very shortened. Still more, individual transmission stations arefree from communications with an extra central station, and adjacentstations are decentrally cooperative to do with processes up to arecovery, permitting complicate communication procedures to be omitted.

With respect to the embodiment 10 (claim 10), FIG. 4 is an example ofconfiguration of transmission station. FIG. 22 shows a flowchart of acorresponding procedure for recovery from a detection of failureoccurrence. The flowchart in FIG. 22 is an example (the 2^(nd) 9) forreconfiguration from one-point failure of a double ring network system,as an example in which a failure occurs between #ST10 and #ST9, and aterminal station waits a timing assigned by a MAC to own station toenable sending RRR frames.

FIG. 19 illustrates a double ring network configured with #ST5 and #ST6as opposing terminal stations, in a situation that, while it is workingnormally, a transmission anomaly has occurred in communication lineinterconnecting #ST10 and #ST9.

There are no restrictions to, among others, the number of transmissionstations or location of occurrence, or relation with positions ofterminal stations or synchronizing station. FIG. 20 illustrates statusof switches at respective transmission stations after occurrence oftransmission anomaly in communication line interconnecting #ST10 and#ST9.

The functions and actions of respective circuits constitutingtransmission stations are identical to functions and actions, such assetting and holding, among others, own station address information andadjacent station address information, excluding the RRR frame receptiondetecting circuit 37 (RRR-DET-A) and RRR frame reception detectingcircuit 39 (RRR-DET-B), with their detection output signals IRP-RRR-A,-B inclusive, and RRR frame destination holding circuit 38, as describedwith respect to the above-noted embodiment 9 (claim 9).

Further, as described with respect to the above-noted embodiment 9(claim 9), the double ring network system has thereon, in addition toSYN frames from a synchronizing station, among others, periodically senttransmission frames and sporadically sent transmission frames fromrespective transmission stations, as they are sent in accordance with atransmission line control system for avoiding collisions betweentransmission frames on a double ring network system as a higher layer ofOSI that is not specifically needed to prescribe for the presentinvention, and under this condition, if transmission anomaly happens incommunication line interconnecting #ST10 and #ST9 as illustrated in FIG.19, then as described with respect to the embodiment 8 (claim 8), SYNabsence will not be detected at #ST10, respective stations #ST2, #ST3,and #ST4 on a route from #ST1 being a synchronizing station to aterminal station #ST5, and #ST5, as they are still able to detectarrival and reception of periodic and consecutive SYN frames from thesynchronizing station.

On the other hand, at #ST9, #ST8, #ST7, and #ST6 on a route between #ST9and a terminal station #ST6, both inclusive, there is a detection of SYNabsence, and a detection of reception anomaly as circumstances permit.Further, at #ST10, detecting periodical arrival and reception of SYNframe, there is a resultant detection of reception anomaly under theabove-noted condition.

For the example of FIG. 19, in the situation that transmission anomalyhas occurred in communication line interconnecting #ST10 and #ST9,respective stations have their switch status shown in FIG. 20. That is,at a step S0 in FIG. 22 for #ST9, #ST8, and #ST7, or at a step S-R0 for#ST6, SW-FW-B is turned off, and SW-REC-B is turned off, so they havethe status O-L-M1 (refer to FIG. 20( c)) or the status T-R-M1 (refer toFIG. 20( b)) shown in FIG. 20, respectively.

Further, for #ST10, at a step S-01, SW-FW-A and SW-REC-A are turned off,so it stands as a new terminal station STT-R. On the other hand, for theterminal station #ST5, although it can detect periodical consecutivearrivals of SYN frames at the port A as a port on the synchronizingstation side, it is unable to detect any arrival of SYN frame at theport B opposing the other terminal station #ST6, whereby it can detectan occurrence of transmission anomaly, substantially simultaneously withthe terminal station #ST6, subject to a lag of signal on a transmissionline.

At a step S-L1, at the port B on the opposite side to the synchronizingstation side, the SW-REC-B is turned on to permit a reception to betaken in, and a program-controlled ST timer is started. ST timer valueat the step S-L1 is set to a greater value than a maximal waiting timefor #ST6 to be permitted to send a transmission frame in compliance withnot specifically defined transmission line control system to avoidcollisions between transmission frames on a double ring network.

Between the two terminal stations, the terminal station #ST6 in asubsequent position on the route from the synchronizing station #ST1 tothe location of anomaly operates, at the step S-R1, to turn the SW-REC-Acorresponding to the port A at the opposite side to the other terminalstation, from OFF to ON, to permit a transmission frame to be receivedand taken in at the port A.

Under this condition, it receives and takes in a sequence oftransmission frames from the other terminal station #ST5 by the MAC/DLC,and determining by the MPU's program control, waits for sending timingsof transmission frames assigned to own station, in compliance with atransmission line control system for avoiding collisions betweentransmission frames on double ring networks. At the step S-R2, as thesending timing Tmac gets a true state, it turns the SW-REC-A from ON toOFF, changing the port A again to a reception-prohibited state, and theSW-REC-B from OFF to ON, changing the port B to a reception-enabledstate, and sends RRR frames addressing #ST5 as a destination from bothports, while starting the ST timer, waiting for reception of an RRRframe addressing own station as a destination from an adjacent station#ST7 on the way to the synchronizing station.

The #ST5 being a SYN normal terminal station, after detection oftransmission anomaly, enters a step S-L21, where it responds toreception of an RRR frame from the SYN absence detecting terminalstation #ST6, by determining own station as being a destination of thereceived RRR frame, and switches an RRR reception port B that has beenin a blocked state as a terminal station, to an unblocked state,changing from the terminal station status to a repeater station normalmode. On the other hand, unless reception occurs till the ST timer thathas been started since before times up, then it returns the SW-REC-B toOFF, holding the terminal station ST-T-L.

Respective transmission stations #ST7, #ST8, and #ST9 functioningnormally on a way from the SYN absence detecting terminal station #ST6to the anomaly occurrence location each have a repeating function heldin this direction, and enter a step S1, where if they receive RRR framessent from #ST6 at a time, though with some transmission route delays,then as own station is not a destination, they each send an RRR framehaving as the destination an address of an adjacent transmission stationon the side of the port A being a reception port of RRR frame, from itsreception port of RRR frame, as it has had the SW-TX-B temporarilyturned off, immediately after a completion of reception of the RRRframe, while starting an ST timer.

The #ST6 enters a step S-R31, where if it receives and detects an RRRframe addressing own station from an adjacent station #ST7 on the port Bside on the way to the synchronizing station before the ST timer timesup, then after a wait till the ST timer times up, it changes the port Bon the side on the way to the synchronizing station that has been in ablocked state since the time of anomaly detection, and the port Aopposing the ST-T-L that has been in a blocked state since before, tounblocked states, rendering both ports reception-enabled, whereby italters from the terminal station status to a repeater station normalmode.

At the transmission station #ST7, #ST8, or #ST9 functioning normally onthe way from the SYN absence detecting terminal station #ST6 to theanomaly occurrence location, after the step S1 where it has sent an RRRframe addressing an adjacent transmission station on the RRR receptionport side as the destination from the RRR reception port side, if itdetects reception of an RRR frame addressing own station from anadjacent transmission station on the way to the synchronizing station atthe step S21 before the ST timer that has been started at the time ofsending times up, then after a wait till the ST timer times up, itchanges the port B that has been in a blocked state since the time ofanomaly detection, to an unblocked state, whereby it comes back to arepeater station normal mode.

On the other hand, at the transmission station #ST9 adjacent to theanomaly location on the way to the SYN absence detecting terminalstation #ST6, as it is failing to receive an RRR frame addressing ownstation from #ST10 even if the ST timer times up, at a step S22, itholds the port B in a blocked sate, so it stands as a new terminalstation ST-T-L. Likewise, also for occurrence of anomaly at a locationadjacent to the SYN absence detecting terminal station, as this isfollowed by absence of reception of an RRR frame addressing own stationover lapse of a preset time, at the step S-R2, it holds a port that hasbeen in a blocked state since the time of anomaly detection, as it isblocked, and changes the other communication port that has been in ablocked state since before as a terminal station, to an unblocked state,whereby it alters from the terminal station St-T-R to an ST-T-L.

By the foregoing, as described with respect to the embodiment 9 (claim9), for occurrence of a transmission anomaly condition due to one-pointfailure on a double ring network system, positions of terminal stationsare changed to a combination of an adjacent station on the way from alocation of anomaly occurrence to a synchronizing station and anadjacent station on the way from the location of anomaly occurrence tothe opposite side, to thereby avoid a total shutdown of the network.Further, terminal stations are re-locatable with a confirmed soundnessof bi-directional communications with adjacent stations, allowing for asubstantially simultaneous single-time completion between transmissionstations on a route to transmission stations to be new terminalstations, permitting the recovery time from anomalous state to recoveryto be very shortened.

Still more, individual transmission stations are free fromcommunications with an extra central station, and adjacent stations aredecentrally cooperative to do with processes up to a recovery,permitting complicate communication procedures to be omitted.

Therefore, according to this embodiment, in a system for initialization,two terminal stations are kept from repeating transmission frames theyreceive, so as not to have transmission frames sent from transmissionstations circulate in a network configured in a ring form, allowing forconfiguration of a logically bus type network.

Further, in view of a master station of which a position on a doublering network is not specifically restricted for initialization,positions of terminal stations are uniquely determined in accordancewith configuration of the network, at the time of initialization of thenetwork.

Further, for the control system, transmission frames to be used premisethe Ethernet® standard, while the SYN frame, RRR frame, INZ frame, orINZ-COMP frame defined in this system are not restricted to any specificframe format, and may be any transmission frame providing that they areidentifiable.

Further, according to this system, an initializing system permits atransmission line up to an adjacent station and an adjacent stationcommunication function, as well as a communication function including atransmission line from the adjacent station to own station to be checkedfor anomaly in each of both directions, allowing for a double ringnetwork to be initialized with transmission lines free of anomaly.

This is by a soundness of bi-directional communication lines possiblyensured between mutually adjacent stations working in unison in theprocess of incorporating transmission stations one by one from an MSstation to a double ring network, where each transmission stationnecessarily receives a responding acknowledgment INZ frame from anadjacent station, subject to a soundness of a reception system on the MSport side, and no anomalies in a transmission line to a transmissionstation adjacent to a port on the opposite side to the MS port, theadjacent station's reception and transmission function, and a returningtransmission line from the adjacent station to own station.

Further, the process of incorporation enables acquisition of addressinformation of adjacent stations of own station, with an extensiveapplication, allowing for a facilitated grasp of connected status oftransmission stations constituting a network, at the time ofinitialization.

Upon occurrence of a transmission anomaly condition due to one-pointfailure on a double ring network system, positions of terminal stationscan be changed to a combination of an adjacent station on the way from alocation of anomaly occurrence to a synchronizing station and anadjacent station on the way from the location of anomaly occurrence tothe opposite side, to thereby avoid a total shutdown of the network.

Further, terminal stations are re-locatable with a confirmed soundnessof bi-directional communications with adjacent stations, allowing for asubstantially simultaneous single-time completion between transmissionstations on a route to transmission stations to be new terminalstations, permitting the recovery time from anomalous state to recoveryto be very shortened.

Still more, individual transmission stations are free fromcommunications with an extra central station, and adjacent stations aredecentrally cooperative to do with processes up to a recovery,permitting complicate communication procedures to be omitted.

(Supplementary Description of Automatic Terminal Station SettingFunction)

The foregoing configuration of double ring network system is to haveprocesses implemented as follows.

FIG. 24 is a flowchart generally describing an automatic terminalstation setting function of a double ring network system according tothis embodiment.

FIG. 25 is an explanatory diagram describing terminal stations set in aninitialization. FIG. 26 is an explanatory diagram describing relocatedterminal stations. In this embodiment, as illustrated in FIG. 25, adouble ring network system is configured with nine transmission stations#ST1 . . . transmission stations #ST9, including #ST1 as a masterstation MS, having #ST5 and #ST6 as terminal stations initially set,using INZ frames, INZ-COMP frames, and the like, as described.

As shown in FIG. 24, the terminal station #ST5 (referred herein to aterminal station LT) and the terminal station #ST6 (referred herein to aterminal station RT) are now assumed to be under an imaginary conditionwith a circuit disconnection on the way to the terminal station RT(S241, S243). That is, the terminal station LT is able to receive aframe from a left-hand transmission station #ST4, but unable to transmitthis to #ST6. Also, the terminal station RT is able to receive a framefrom a right-hand transmission station #ST7, but unable to transmit thisto #ST5.

And, the terminal station LT checks if it has received a SYN frame fromthe left-hand #ST4 (S245). Also, the terminal station RT checks if ithas received a SYN frame from the right-hand #ST7 (S247).

Then, the terminal station LT as well as RT slips out of terminalstation, unless it receives a SYN frame within a prescribed time (S249,S251). That is, #ST6 as well as #ST5 slips out of terminal station, sothat if it be #ST6 this is enabled to transmit a frame to #ST5, and ifit be #ST5 this is enabled to transmit a frame to #ST6.

On the other hand, the master station MS as a base (referred hereinsometimes to a synchronizer) transmits SYN frames in both directions(right-handed, left-handed transmission) to respective transmissionstations (S253). A respective transmission station receives such a SYNframe at a communication port A on one side, or a communication port onthe other side (S255).

And, other transmission stations each check if SYN frames are receivedin both directions (S257).

For instance, as illustrated in FIG. 3, each transmission station isprovided with a SYN frame detecting circuit 34 (SYN-DET-A) and a SYNframe detecting circuit 36 (SYN-DET-B), whereby reception of SYN frameis verified to detect, and output as an IRP-SYN-A signal representing aright-hand reception, or an IRP-SYN-B signal representing a left-handreception.

Further, there is a SYN absence detecting circuit 35 (NO-SYN-DET-A/-B),which outputs an IPR-NO-SYN if it fails to input consecutiveIRP-SYN-A/-B.

Accordingly, given consecutive IRP-SYN-A outputs, an MPU 24 is informedof consecutive SYN frames input through a communication port on oneside. Further, given an IRP-NO-SYN output following an IRP-SYN-B output,it is informed of absence of periodical consecutive arrivals inputthrough a communication port on the other side over a prescribedinterval.

Further, the MPU 24 detects an anomaly in reception signal status of atransmission frame received through communication port A or -B fromRCV-ERR-A or -B, depending on criteria to determine a monitoringreception signal status as being anomalous, as described.

That is, at the step S257, it determines having failed to receive SYNframes in both directions. In failure of reception of SYN frames in bothdirections, other transmission stations each send RRR frames in bothdirections (S259).

In this embodiment, it is assumed that #ST8 has failed to receive SYNframes from #ST9, and #ST9 has failed to receive SYN frames from #ST8.

#ST8 transmits RRR frames to both #ST9 and #ST7, and #ST9 transmits RRRframes to both #ST8 and #ST1.

Transmission stations (#ST9, #ST7) adjacent to #ST8 as well astransmission stations (#ST8, #ST1) adjacent to #ST9 are each adaptedupon reception of an RRR frame, to send RRR frames in both directions,and upon a failed reception of an RRR frame, not to send RRR frames(S261).

On the other hand, transmission station #ST8 as well as transmissionstation #ST9, as having sent RRR frames, checks if it receives an RRRframe from the adjacent transmission station (S263).

At the step S263, if #ST8 as well as #ST9 determines no RRR frame ashaving been received from the adjacent station having received an RRRframe, then it determines a way to the adjacent station #ST9 or #ST8 asbeing anomalous (S265). With this determination, #ST8 as well as #ST9stands as a terminal station, as illustrated in FIG. 26 (S276).

That is, it has a function not to transmit a frame from the base to anadjacent transmission station failing to respond even though it has sentan RRR frame thereto.

It thus so follows that according to this embodiment each transmissionstation in the double ring network system has an automatic terminalstation setting means 50 shown in FIG. 27. In this embodiment, it isdepicted at representative #ST3 and #ST6.

The automatic terminal station setting means 50 includes an own stationterminal setting means 52, a terminal station canceling means 54, aframe transmitting means 58, etc.

The own station terminal setting means 52 determines whether or not SYNframes are consecutively input from an adjacent station, and unless theyare consecutively input, it sets up in a memory 56 a flag representing away to the adjacent station as being anomalous. If the flag representinga way to the adjacent station as being anomalous is set up in the memory56, the frame transmitting means 58 transmits RRR frames to bothadjacent transmission stations, and informs the own station terminalsetting means 52 of the transmission of RRR frames.

The own station terminal setting means 52 determines whether or not anRRR frame is received, and unless an RRR frame is received, it sets upin the memory 56 a flag representing own station as being set as aterminal station.

If own station is set as a terminal station, the frame transmittingmeans 58 is kept, even when receiving a SYN frame from the base, fromsending this to a subsequent transmission station.

If SYN frames are consecutively input from both adjacent transmissionstations, the terminal station canceling means 54 operates to have theframe transmitting means 58 transmit RRR frames to the adjacenttransmission stations, and respond to an RRR frame as a return, bydeleting from the memory 56 the flag representing own station as beingset as a terminal station.

(Detailed Description)

There will be described an embodiment of the present invention intodetails.

Description is now made of a transmission station according to thepresent embodiment, with reference to FIG. 3 as an example. In FIG. 3,the transmission station is made up by a section of communication port10 (port A), a communication port 11 (port B), a transmission receptionpermitting switch section 9, a first-come reception control circuit 20(RCV-SEL), a transmission reception control circuit 21 (MAC/DLC), acomputer section 30, a frame detection determiner 31, and the like.

The communication port section 10 (port A) is configured with a receiver(RVR-A) and a transmitter (TVR-A) to implement bi-directionalcommunications with an adjacent station (a left adjacent station, forinstance).

The communication port section 11 (port B) is configured with a receiver(RVR-B) and a transmitter (TVR-B) to implement bi-directionalcommunications with an adjacent station (a right adjacent station, forinstance).

The transmission reception permitting switch section 9 includes arepeater 12 (FW-A: referred also to a repeater A), a repeat permittingswitch 13 (SW-FW-A), a repeat permitting switch 14 (SW-FW-B), a repeater15 (FW-B: referred also to a repeater B), a transmission permittingswitch 16 (SW-TX-A), a transmission permitting switch 17 (SW-TX-B), areception permitting switch 18 (SW-RCV-A), a reception permitting switch19 (SW-RCV-B), and the like.

The computer section 30 is configured with an IOC 22, an IRP 23, an MPU24, a PROM/RAM 25, a DP/RAM 26, a DPRC 27, a HOST-IF 28, and the like.The HOST-IF 28 is adapted for communications with a host device 29.

And, the frame detection determiner 31 has a plurality oflater-described circuits to determine types and anomalies of frames.

It includes a reception anomaly detecting circuit 32 (RCV-ERR-A), areception anomaly detecting circuit 33 (RCV-ERR-B), a SYN framedetecting circuit 34 (SYN-DET-A), a SYN absence detecting circuit 35(NO-SYN-DET-A/B), a SYN frame detecting circuit 36 (SYN-DET-A), and anRRR frame reception detecting circuit 37 (RRR-DET-A).

Further, it is configured with an RRR frame destination address holdingcircuit 38 (RRR-RCV-ADRS), an RRR frame reception detecting circuit 39(RRR-DET-B), an INZ frame reception detecting circuit 40 (INZ-DET-A), anINZ frame source address holding circuit 41 (INZ-TX-ADRS-A), an INZframe reception detecting circuit 42 (INZ-DET-B), an INZ frame sourceaddress holding circuit 43 (INZ-TX-ADRS-B), and the like.

The above-noted RVR-A (receiver A: for reception at the left, with abase station on the left) of the communication port 10 is adapted tooutput a received signal as an SIG-RV-A reception signal.

And, the RVR-B (receiver B: for reception of signals from a clockwisedirection) of the communication port 11 is adapted to output a receivedsignal as an SIG-RV-B reception signal.

On the other hand, the TRV-A of the communication port 10 is adapted tosend a reception signal from the repeat permitting switch 14 (SW-FW-B)(a reception signal as received at the RVR-B of the communication port11 and relayed through the repeater B) or a signal from the transmissionpermitting switch 16 (SW-TX-A), as a transmission signal A to atransmission line.

And, the TRV-B of the communication port 11 is adapted to send areception signal from the repeat permitting switch 13 (SW-FW-A) (areception signal as received at the RVR-A of the communication port 10and relayed through the repeater A) or a signal from the transmissionpermitting switch 17 (SW-TX-B), as a transmission signal B to atransmission line.

The repeater A is connected with the RVR-A of the communication port 10and to the repeat permitting switch 13 (SW-FW-A), and adapted to send anSIG-RVR-A reception signal received at the RVA-A to the repeatpermitting switch 13 (SW-FW-A).

The repeat permitting switch 13 (SW-FW-A) is connected to the TRV-B(transmitter B) of the communication port 11, and adapted, if set to anon state, to output a received SIG-RVR-A reception signal to the TRV-Bof the communication port 11.

The repeat permitting switch 14 (SW-FW-B) is connected to the TRV-A(transmitter A) of the communication port 10, and adapted, if set to anon state, to output a received SIG-RVR-B reception signal to the TRV-Aof the communication port 10.

As an output of the above-noted RVR-A, the SIG-RV-A signal from the portA is output, besides the repeater A (FW-A), as illustrated in FIG. 3, tothe reception permitting switch 18 (SW-RVC-A), and the reception anomalydetecting circuit 32 (RCV-ERR-A), SYN frame detecting circuit 34(SYN-DET-A), and RRR frame reception detecting circuit 37 (RRR-DET-A) inthe frame detection determiner 31.

Further, it is sent to the RRR frame destination address holding circuit38 (RRR-RCV-ADRS), the INZ frame reception detecting circuit 40(INZ-DET-A), and the INZ frame source address holding circuit 41(INZ-TX-ADRS-A).

Likewise, upon a reception at the port B being the other section ofcommunication port 11, as an output of the RVR-B, the reception signal(SIG-RV-B) from the port B is output to the repeater B (FW-B), thereception permitting switch 19 (SW-RCV-B), the reception anomalydetecting circuit 33 (RCV-ERR-B), the SYN frame detecting circuit 36(SYN-DET-B), and the RRR frame reception detecting circuit 39(RRR-DET-B).

Further, it is sent to the RRR frame destination address holding circuit38 (RRR-RCV-ADRS), the INZ frame reception detecting circuit 42(INZ-DET-B), and the INZ frame source address holding circuit 43(INZ-TX-ADRS-B).

(Description of Circuits)

The transmission permitting switch 16 (SW-TX-A) is adapted, when in apermitting state ON, to send a transmission output signal (transmissionframe) of the transmission reception control circuit 21 (MAC/DLC) to theTVR-A of the port A being the one section of communication port 10. And,it is adapted, when in an OFF, for a switching to cut transmissionoutput signals of the MAC/DLC, and as a result, no transmission frame issent from the TVR-A of the communication port 10 corresponding thereto.

The transmission permitting switch 17 (SW-TX-B) is adapted, when in anON, to send a transmission output signal (transmission frame) of thetransmission reception control circuit 21 (MAC/DLC) to the TVR-B of theother section of communication port 11. And, it is adapted, when in anOFF, for a switching to cut transmission output signals of thetransmission reception control circuit 21 (MAC/DLC), and as a result, notransmission frame is sent from the TVR-B of the communication port 11corresponding thereto.

The reception permitting switch 18 (SW-RCV-A) is adapted to input anSIG-RV-A reception signal, and output a frame of this reception signalto the first-come reception selecting circuit 20 (RCV-SEL).

The reception permitting switch 19 (SW-RCV-B) is adapted to input anSIG-RV-B reception signal, and output a frame of this reception signalto the first-come reception selecting circuit 20 (RCV-SEL).

The first-come reception selecting circuit 20 (RCV-SEL) is adapted todetermine a frame as from the reception permitting switch 18 (SW-RCV-A)and a frame as from the reception permitting switch 19 (SW-RCV-B), andif an overlap is found in between, to make a selection for a receptionto be completed with a priority to a reception signal (transmissionsignal) received at the port side where either has first come.

An output of the RCV-SEL is lead to the transmission reception controlcircuit 21 (MAC/DLC), where it is processed for reception. According tothe present embodiment, a double ring network system is configured in aring form, nonetheless, to be equivalent to a bus type network, whileworking in a sound state, and the transmission reception control circuit21 (MAC/DLC) is adapted, at transmission stations except for terminalstations, to have either port receive a transmission frame at a time,depending on positional relations between own station and transmissionframe sending stations.

The transmission reception control circuit 21 (MAC/DLC) is adapted tocontrol transmission and reception of signals (SIG-RV-A, SIG-RV-B) oftransmission frames compliant with Ethernet® protocol, and sendtransmission outputs of the transmission reception control circuit 21(MAC/DLC) to the transmission permitting switch 16 (SW-TX-A) and thetransmission permitting switch 17 (SW-TX-B).

Further, it is adapted to output an IRP-DLC (a detection signal ofcompletion of transmission or reception of MAC/DLC) to the IRP 23 in thecomputer section 301.

The computer section 30 has a function to control ON and OFF stateswitching of the above-noted reception permitting switches, transmissionpermitting switches, and repeat permitting switches.

The MPU 24 is configured as a core microprocessor, which followsprocedures of programs stored in (a PROM among) program memories(employing the PROM, a working RAM memory, and a RAM), reading setvalues as necessary, and writing necessary data, temporarily holding orreading, to implement processes of, among others, Ethernet® transmissionprotocol and sequence procedures at transmission stations according tothe present invention.

The IOC 22 is configured as an input output control circuit forreceiving written data from the MPU 24 to output control signals torequiring circuits, or for receiving status inputs of respectivecircuits for the MPU 24 to read.

An interrupt signal detecting circuit 23 (the IRP) is configured as acircuit for detecting interrupt signals as signals interrupting toinform the MPU 24 of occurrences of events detected in circuitry oftransmission station.

Enumerative as interrupt signals are those by detection of: occurrencesof reception anomaly (IRP-RE-A, IRP-RE-B), absence of SYN (IRP-NO-SYN),reception of SYN frames (IRP-SYN-A, IRP-SYN-B), reception of RRR frames(IRP-RRR-A, IRP-RRR-B), reception of INZ frames (IRP-INZ-A, IRP-INZ-B),and completion of MAC/DLC transmission or reception (IRP-DLC).

Further, enumerative are such as those for requests for processing(IRP-STN) from the IOC 22 to the host device, and requests forprocessing (IRP-HOST) from the MPU to the host device.

The IRP 23 has an IRP-DLC signal input thereto from the transmissionreception control circuit 21 (MAC/DLC), and as will be described lateron, it has input from the frame detection determiner 31, an IRP-RE-A(reception anomaly occurrence signal A), an IRP-RE-B (reception anomalyoccurrence signal B), an IRP-NO-SYN (SYN absence detecting signal), anIRP-SYN-A (SYN frame reception detecting signal A), an IRP-SYN-B (SYNframe reception detecting signal B), an IRP-RRR-A (RRR frame receptiondetecting signal A), an IRP-RRR-B (RRR frame reception detecting signalB), an IRP-INZ-A (INZ frame reception detecting signal A), and anIRP-INZ-B (INZ frame reception detecting signal B), and the IRP-DLC(MAC/DLC transmission reception completion detecting signal) andIRP-HOST’ (processing request signals) to the host, alone or incombination of inputs, whereto it responds by outputting to the MPU 24an interrupt informing what anomaly is detected.

The IRP-RE-A and the IRP-RE-B are collectively referred to as areception anomaly occurrence detecting signal, and the IRP-SYN-A and theIRP-SYN-A-B are collectively referred to as a SYN frame receptiondetecting signal.

Further, the IRP-RRR-A and the IRP-RRR-B are collectively referred to asan RRR frame reception detecting signal, and the IRP-INZ-A and theIRP-INZ-B are collectively referred to as an INZ frame receptiondetecting signal.

A C-bus constitutes a common data bus connected to the MPU 24, andthrough the C-bus, the MPU 24 is adapted to read, among others, adetected status in particular of the SYN absence detecting circuit 35(NO-SYN-DET-A/B), pieces of RRR frame destination address informationheld in the RRR frame destination address holding circuit 38(RRR-RCV-ADRS), and pieces of INZ frame source address information heldin the INZ frame source address holding circuit 41 (INZ-TX-ADRS-A) andthe INZ frame source address holding circuit 43 (INZ-TX-ADRS-B).

The DP-RAM 26 is a dual-port memory circuit, which is configured forstorage of data on transmission frames received or to be transmitted atthe MAC/DLC, and as a host linking interface circuit 28 for an externalhost device 29 linked with the transmission station (as a memory circuitfor exchange of condition status, and control commands, as well as fordata to be transmitted or received through the HOST-IF).

The DP RAM 26 is accessed from the MPU 24, HOST-IF 28, and MAC-DLC 21,and a DPRAM controller has reading and writing timings controlled by theDPRC 27.

The before-mentioned programs operate in the double ring network system,which is configured in a ring form, nonetheless, to be equivalent to abus type network, while working in a sound state, and for transmissionstations else than terminal stations, they have processes executed tooutput a command to the repeat permitting switch 13 (SW-FW-A) or therepeat permitting switch 14 (SW-FW-B), to receive a transmission frameat either port at a time, depending on positional relations between ownstation and transmission stations sending transmission frames.

For terminal stations where connections remain in a ring form andtransmission frames to be received appear at both ports, they haveprocesses executed to send commands to render the reception permittingswitch off at the port side normally in a blocked state, allowing areception of input at the port side in an unblocked state.

The reception anomaly detecting circuit 32 (RCV-ERR-A) is a circuit fordetecting a reception anomaly corresponding to the communication port 10(port A). That is a circuit for detecting an error of an SIG-RV-Areception signal from the communication port 10 (port A), and uponanomaly detection, operates to output an IRP-RE-A signal (referredsometimes to a reception anomaly detecting signal A) to the computersection 30.

The reception anomaly detecting circuit 33 (RCV-ERR-B) is a circuit fordetecting a reception anomaly corresponding to the communication port 11(port B). Upon detection of reception anomaly, it sends an IRP-RE-Asignal to the computer section 30. In other words, it is a circuit fordetecting an error of an SIG-RV-B reception signal from thecommunication port 11 (port B), and upon anomaly detection, operates tooutput the IRP-RE-B signal (reception anomaly detecting signal B) to thecomputer section 30.

The reception anomaly may be reception of preamble patterns as receptionclock synchronizing signals typical to Ethernet®, greater in number thanspecified, having dividable carrier signals of arrived frames.

To the contrary, there may be an occurrence of detection anomalydetermined by detection of consecutive reception errors greater innumber than specified, such as errors greater in number than specifiedas consecutively detected by checks to an error detection code (FCS) oftransmission frame provided for Ethernet® transmission frames, orfailures in detection of a required preamble pattern, while fordetection circuits the range excludes FCS check means provided for theDLC/MAC and a static processing of results thereof by the MPU 24.

The SYN frame detecting circuit 34 (SYN-DET-A) is a circuit fordetecting an arrival of SYN frame corresponding to the communicationport 10 (port A).

That is, the SYN frame detecting circuit 34 (SYN-DET-A) is a circuitadapted, if an SIG-RV-A reception signal from the communication port 10is a SYN frame, to detect this, and upon detection of a SYN frame, tooutput an IRP-SYN-A signal (referred sometimes to a SYN frame detectingsignal A) to the computer section 30 and to the SYN absence detectingcircuit 35 (NO-SYN-DET-AB).

The SYN frame detecting circuit 36 (SYN-DET-B) is a circuit fordetecting an arrival of SYN frame corresponding to the communicationport 11 (port B). That is, the SYN frame detecting circuit 36(SYN-DET-B) is a circuit adapted, if an SIG-RV-B reception signal fromthe communication port 11 is a SYN frame, to detect this, and upondetection of a SYN frame, to output an IRP-SYN-B (referred sometimes toa SYN frame detecting signal B) to the computer section 30 and to theSYN absence detecting circuit 35 (NO-SYN-DET-A/B).

On the other hand, the SYN absence detecting circuit 35 (NO-SYN-DET-A/B)is a circuit for detecting an occurrence of a long duration of aSYN-free silent state. That is, the SYN absence detecting circuit 35(NO-SYN-DET-A/B) is adapted, unless an IRP-SYN-A signal (SYN framereception detecting signal A) from the SYN frame detecting circuit 34(SYN-DET-A) or an IRP-SYN-B signal (SYN frame reception detecting signalB) from the SYN frame detecting circuit 36 (SYN-DET-B) is output withina certain interval of time, to output an IRP-NO-SYN signal (SYN absencedetecting signal) to the computer section 30.

The RRR frame reception detecting circuit 37 (RRR-DET-A) is a circuitfor detecting a reception of an RRR frame corresponding to thecommunication port 10 (port A). In other words, it is adapted to detectan RRR frame (a signal informing a detection of a disconnection) in anSIG-RV-A reception signal from the RVR-A of the communication port 10(port A), and upon detection, to output an IRP-RRR-A signal (RRR framereception detecting signal A) to the computer section 30.

The RRR frame reception detecting circuit 39 (RRR-DET-B) is a circuitfor signal detection to detect a reception of an RRR frame correspondingto the communication port 11 (port B). In other words, it is adapted todetect an RRR frame in an SIG-RV-B from the RVR-B of the communicationport 11 (port B), and upon detection, to output an IRP-RRR-B signal (RRRframe reception detecting signal B) to the computer section 30.

The RRR frame destination address holding circuit 38 (RRR-RCV-ADRS) is acircuit for taking in, to hold, a field of destination address (DA) ofan RRR frame in an SIG-RV-B signal received at the communication port 11(port B), and is adapted to output a signal of H level, for instance, tothe C-bus, when with the field. The RRR destination address holdingcircuit 38 (RRR-RCV-ADRS) has a circuit configuration adapted to take inreception signals at both sides, taking timings to take in destinationaddress fields.

The INZ frame reception detecting circuit 40 (INZ-DET-A) is a circuitfor detecting a reception of an INZ frame corresponding to the port A.That is, when having detected an INZ frame in an SIG-RV-A signalreceived at the communication port 10 (port A), it outputs an IRP-INZ-A(INZ frame reception detecting signal A) to the computer section 30.

The INZ frame reception detecting circuit 42 (INZ-DET-B) is a circuitfor signal detection to detect a reception of an INZ frame correspondingto the communication port 11 (port B). That is, when having detected anINZ frame in an SIG-RV-B signal received at the communication port 11(port B), it outputs an IRP-INZ-B (INZ frame reception detecting signalB) to the computer section 30.

The INZ frame source address holding circuit 41 (INZ-TX-ADRS-A) is acircuit corresponding to the port A, and adapted to hold a field ofsource address (SA) of an INZ frame in an SIG-RV-A signal received atthe port A.

The INZ frame source address holding circuit 43 (INZ-TX-ADRS-B) is acircuit corresponding to the port B, and adapted to hold a field ofsource address (SA) of an INZ frame in an SIG-RV-B signal received atthe port B.

Stations are configured as described above, and incorporated in a doublering network, as illustrated in FIG. 1.

For stations configured as above, an initializing process will bedescribed.

For the initialization, as illustrated in FIG. 28,

in a double ring network system including a plurality of transmissionstations having any one thereof as a base station, and each respectivelyconnected by a dual transmission line composed of a first communicationline and a second communication line, the respective transmissionstation being provided with a first communication port for receiving atone end side (right-hand end) thereof left-handed information from thebase station and outputting right-handed input information from the basestation or information generated at this station in a right-handeddirection from the one end side (right-hand end), and a secondcommunication port for receiving at another end side (left-hand end)thereof right-handed input information from the base station andoutputting the left-handed information or information generated at thisstation in a left-handed direction from the other end side (left-handend), to perform bi-directional communications in between,

the base station has, for an initial phase of startup,

an INZ frame transmitting means (initializing signal sending means 63)for transmitting right-handed and left-handed initializing first framescontaining information having a source as the base station and adestination of transmission station designated, simultaneously from thefirst communication port and the second communication port. Preferably,the other stations should also have this initializing signal sendingmeans 63.

The other stations have, for the initial phase of startup,

an INZ frame reception permitting means (implemented in FIG. 28 with aninitializing completion responding means 61, a switch group controllingmeans 62, and a switch controlling means 62) for permitting reception ofinformation from the first communication port and the secondcommunication port,

a first-come determining means (configured in FIG. 28 with a first-comereception selecting circuit 20) for determining, when the first framesare received at the first communication port and the secondcommunication port, the communication port having first-received saidfirst frame,

an own station position identifying means (71 in FIG. 28) fordetermining, when the right-handed and left-handed first frames havingthis station as a destination are received the right-handed at the firststation and the left-handed at the second station, respectively, thestation being positioned at a left-handed end or a right-handed end,whichever is in accordance with line lengths from the base station tothis station and identification information of respective stations theright-handed and left-handed routed through as contained in the firstframes, and outputting a terminal station setting signal to have set ifit stands as a terminal station on either hand,

a first terminal station deciding means for operating with the terminalstation setting signal output, for a result of the first-comedetermination that the first communication port has first received theright-handed first frame, to set the own station in a terminal stationmode at a left-hand end from the base station, transmit the left-handedfirst frame the second communication port has received temporarily to aleft-hand adjacent station, and thereafter, stop sending informationfrom the second communication port, and

a second terminal station deciding means for operating with the terminalstation setting signal output, for a result of the first-comedetermination that the second communication port has first received thefirst frame, and the first communication port has received theleft-handed first frame from a right-hand adjacent station, to set theown station to be a terminal station mode at a right-hand end from thebase station, and stop sending information from the first communicationport. The first and second terminal station deciding means areimplemented in FIG. 28 with a repeat station/terminal station modesetting means 68.

In FIG. 28, along with the startup, the initializing signal sendingmeans 63 has a frame sending means 69 send an INZ frame. The framesending means 69 reads an address of own station and an address of asource of reception from a memory 70, and incorporates them in the frameto be sent out.

On the other hand, along with the initializing signal sending means 63sending an INZ frame, the switch group controlling means 62 reads a setof switch setting data at the time of initialization from the switchtable 64, having an outputting means 65 output the same. There are setsof switch setting data shown in FIG. 6, FIG. 7, and FIG. 20. Respectiveswitches are controlled to turn on or off in accordance with the set ofswitching data.

And, the own station position identifying means 71 reads frames receivedat SW-RCV-A and SW-RCV-B, and identifies a position of own station fromthe own station address in the memory 70 and source addresses oftransmitted frames. Based on the position thus identified, the repeaterstation/terminal station mode setting means 68 operates for a setting tobe a repeater station or terminal station, having a timer 67 to start.

Then, the initializing completion responding means 66 operates, for therepeater station or terminal station set at the time of initialization,to have the frame sending means 69 send an initializing completionframe.

FIG. 29 is a complementary sequence chart to FIG. 9 showing sequences ofINZ frames between transmission stations communicating with each at thetime of initialization.

In the sequence chart of FIG. 29, a master station MS (transmissionstation #ST1) transmits INZ frames for initialization in a left-handdirection (transmission station #ST2, . . . , transmission station#ST4), and in a right-hand direction (transmission station #ST8, . . . ,transmission station #ST5).

In other words, the MPU 24 operates as an INZ frame transmitting meansfor an initializing process for setting the transmission permittingswitch 16 (SW-TX-A) in an on state and setting the transmissionpermitting switch 17 (SW-TX-B) in an on state, to bi-directionallytransmit INZ frames from the transmission reception controller 21(MAC/DLC).

Then, at a respective transmission station, the MPU 24 is operating as aframe reception detecting means adapted for setting the receptionpermitting permission switch 18 (SW-RCV-A) and the reception permittingswitch 19 in on states, to have incoming INZ frames from bothcommunication ports taken into the first-come reception selectingcircuit 20 (RCV-SEL), and a result thereof input to the transmissionreception controller 21 (MAC/DLC).

This determination of first-come may involve a case of framessimultaneously input to the communication port A and the communicationport B, depending such as on numbers of stations and line lengths ofrouted lines. In such the case, a predetermined side may preferably bedetermined as first-come.

Further, for initializing frames to be detected, the detection isperformed by the INZ frame reception detecting circuit 40 (INZ-DET-A)and the INZ frame reception detecting circuit 42 (INZ-DET-B). The framereception detecting means includes the INZ frame reception detectingcircuit 40 (INZ-DET-A) and the INZ frame reception detecting circuit 42(INZ-DET-B).

In FIG. 29, #ST5 receives R-handed from (the communication port A) anINZ frame (destined for #ST5) from the master station through #ST8,#ST7, and #ST6 (encircled “1” in FIG. 29), and an INZ frame (destinedfor #ST5) from the master station (MS) L-handed arrives at the #ST5through #ST2, #ST3, and #ST4 (encircled “2” in FIG. 29). That is, itreceives (da) a pair of INZ frames.

And, for the INZ frames having arrived R-handed and L-handed at #ST5, asthe INZ frames contain respective routed stations' addresses, it cancount their numbers, to thereby get where is own station in right-handedand left-handed orders.

Further, in response to the INZ frames, it sends respondingacknowledgment frames, counting their times, and from points of timewhen the frames are looped around, it can get (R-handed and L-handed)line lengths from own station to the master station. This process isimplemented by the own station position identifying means (refer to FIG.10 and FIG. 11).

Next, after the identification of its position, it transmits (db) anINZ-COMP frame R-handed to the master (MS station), informing of itsbeing set as a terminal station in the initial setting. That is,initially for an INZ frame it has received first at the communicationport A (R-handed) before reception at the communication port B(L-handed), it operates as an R-handed terminal to transmit the INZ-COMPR-handed to the master MS.

This determination of whether the communication port A has firstreceived or the communication port B has first received is implementedby the first-come reception selecting circuit 20 (RCV-SEL).

Further, the #ST5 is set after it has sent the INZ-COMP R-handed to themaster (MS), so as not to repeat any INZ frame, if this INZ frame issent R-handed from the master station (MS station) (not to output fromthe communication port B: terminal station deciding means). Forinstance, the repeat permitting switch 13 (SW-FW-A) is set to an offstate.

On the other hand, for #ST6, at the time of initialization, an INZ frameis transmitted R-handed from the master station (MS) to #ST6, asindicated at triangular mark “1” in FIG. 29. From the master station(MS), an INZ frame is transmitted L-handed to the #ST6 (dc).

This L-handed INZ frame arrives at #ST4, #ST5, and #ST6 due tointerconnection between #ST4 and #ST5. Here, the INZ frame of currenttime is let to pass through #ST5.

In other words, at the #ST6, reception of INZ frame is to occur twicebeing R-handed and L-handed (triangular mark “2” in FIG. 29). By that,it operates as a terminal station (R-handed) to transmit (dd) anINZ-COMP frame to the master station (MS). Accordingly, there appear anR-handed terminal station set to be #ST5 and an L-handed terminalstation set to be #ST6.

For the decision of R-handed terminal station and L-handed terminalstation,

each transmission station is adapted to grasp addresses of respectivetransmission stations on the network. For instance, at the communicationport A as a first-come, this frame may have been transmitted with thenumber or addresses of routed stations till this station added, and atthe communication port B, a received frame may have been transmittedwith the number or (forward ordered) addresses of routed stations tillthis station added, allowing own position to be identified in anentirety of network. In this situation, the decision of an R-hand and anL-hand may preferably be reached in consideration of an entire linelength of network and lengths from this station to the master station.

In the case of a frame containing addresses of routed stations, theremay also be a determination of whether an adjacent station has a youngernumber or an older number than own.

For the initializing process of transmission stations, supplementaldetailed description will be made with reference to FIG. 10 and FIG. 11.

FIG. 10 includes a step S101, which is a process for a transmissionstation to bi-directionally transmit (R-handed and L-handed) INZ frames(S01 and S02 in FIG. 10).

Description is now made of a step S0 shown in FIG. 10.

More specifically,

at the step S01, it is determined if INZ frame reception is detected,reception port A (communication port A) is a blocked state, and MSport=B is false, and terminal station=false. . . . First condition.

That is, the computer section 30 is operating to determine if thecondition of S01 is met as shown in FIG. 6, with the repeat permittingswitch 13 (SW-FW-A) set to be off, the repeat permitting switch 14(SW-FW-B), to be off, the transmission permitting switch 16 (SW-TX-A),to be on, the transmission permitting switch 17 (SW-TX-B), to be on, thereception permitting switch 18 (SW-RCV-A), to be off, and the receptionpermitting switch 19 (SW-RCV-B), to be off.

By the setting shown in FIG. 6, transmission output signals from thetransmission reception control circuit 21 (MAC/DLC) are transmittedthrough the transmission permitting switch 16 (SW-TX-A), from the TVR-Aof communication port A to a transmission line, and through thetransmission permitting switch 17 (SW-TX-B), from the TRV-B ofcommunication port B to a transmission line. For the base station (at MSstation, the setting is performed by workers), transmission outputsignals from the transmission reception control circuit 21 (MAC/DLC)have respective transmission stations' addresses contained therein. Bydoing so, sequences shown in FIG. 9 and FIG. 29 are implemented.

The MPU 24 operates

for turning the SW-FW-A or B on to thereby set an unblocked state,simultaneously turning the SW-RCV-A or B on to permit thereaftertransmission frames to be taken in from the reception port.

Moreover, it temporarily turns on simply the SW-TX-A or B correspondingto the reception port, to send a responding acknowledgment frame at thereception port side, and set the station mode to a not terminal.

Further, it receives an INZ frame from a port to be blocked in asituation with an MS port established, to thereby decide terminalstations ST-T-L and ST-T-R in accordance with the reception port.

For the condition of step S01 in FIG. 10,

the MPU 24 in the computer section 30 (referred herein simply to acomputer section 30) sets an address of the MS station to a sourceaddress, and holds the reception port A (communication port A) as it is(adapted to take in a signal through the communication port A).

The computer section 30 turns on the repeat permitting switch 13(SW-FW-A) and the reception permitting switch (SW-RCV-A). That is, areception signal from the communication port

A is repeated through the repeat permitting switch 13 (SW-FW-A) to thecommunication port 11, and a reception signal (SIG-RV-A) from thecommunication port 10 is input by the reception permitting switch(SW-RCV-A) to the first-come reception selecting circuit 20 (RVC-SEL),to determine whether it is a first-come or not, of which a result isoutput to the transmission reception control circuit 21 (MAC/DLC).

Further, the computer section 30 turns the transmission permittingswitch 17 (SW-TX-B) off, and the transmission reception control circuit21 (MAC/DLC) sends an INZ frame (destination is MS station) from the MSport=A (communication port A). Further, in accordance with aninstruction from the computer section 30, the transmission receptioncontrol circuit 21 (MAC/DLC) turns the transmission permitting switch 17(SW-TX-B) on, rendering a reception signal from the port Breception-enabled, to output this to the first-come reception selectingcircuit 20 (RVC-SEL), to determine if it is a first-come. The CPU in thecomputer section 30 then sets the station mode for terminal station tonot (negation).

On the other hand, an SIG-RV-A reception signal received at the port Aundergoes a determination for detection by the frame detectiondeterminer 31. The determination for detection by the frame detectiondeterminer 31 outputs an IRP-RE-A signal (referred sometimes to areception signal A anomaly detecting signal) to the computer section 30,if the reception anomaly detecting circuit 32 (RCV-ERR-A) detects ananomaly of SIG-RV-A reception.

If the SIG-RV-A reception signal from the communication port 10 is a SYNframe, the SYN frame detecting circuit 34 (SYN-DET-A) outputs anIRP-SYN-A signal (referred sometimes to a SYN frame detecting signal A)to the computer section 30, and the SYN absence detecting circuit 35(NO-SYN-DET-A/B).

The RRR frame reception detecting circuit 37 (RRR-DET-A) responds todetection of an RRR frame in an SIG-RV-A from the RVR-A of thecommunication port 10 (port A), by outputting an IPR-RRR-A signal (RRRframe reception detecting signal A) to the computer section 30.

If the INZ frame reception detecting circuit 40 (INZ-DET-A) detects anINZ frame in an SIG-RV-A signal received at the communication port 10(communication port A), it outputs an IRP-INZ-A (INZ frame receptiondetecting signal A) to the computer section 30.

The INZ frame source address holding circuit 41 (INZ-TX-ADRS-A) holds afield of source address (SA) of an INZ frame in an SIG-RV-A signalreceived at the port A.

Further, if the reception anomaly detecting circuit 33 (RCV-ERR-B)detects an anomaly of an SIG-RV-B reception signal from thecommunication port 11 (port B), it outputs an IRP-RE-B (receptionanomaly occurrence detecting signal) to the computer section 30.

If the SIG-RV-B reception signal from the communication port 11 is a SYNframe, the SYN frame detecting circuit 36 (SYN-DET-B) outputs anIRP-SYN-B signal (referred sometimes to a SYN frame detecting signal B)to the computer section 30, and the SYN absence detecting circuit 35(NO-SYN-DET-A/B).

On the other hand, the SYN absence detecting circuit 35 (NO-SYN-DET-A/B)outputs an IRP-NO-SYN signal (SYN absence detecting signal) to thecomputer section 30, if neither IRP-SYN-A signal (SYN-frame receptiondetecting signal A) from the SYN frame detecting circuit 34 (SYN-DET-A)nor IRP-SYN-B signal (SYN-frame reception detecting signal B) from theSYN frame detecting circuit 36 (SYN-DET-B) is output within a presettime.

The RRR frame reception detecting circuit 39 (RRR-DET-B) detects an RRRframe in an SIG-RV-B from the RVR-B of the communication port 11 (portB), and responds to the detection by outputting an IPR-RRR-B signal (RRRframe reception detecting signal B) to the computer section 30.

The RRR frame destination address holding circuit 38 (RRR-RCV-ADRS)takes in and holds a field of destination address (DA) of an RRR framein an SIG-RV-B signal received at the communication port 11 (port B).

The RRR destination address holding circuit 38 (RRR-RCV-ADRS) takes inreceptions signals at both sides, and takes in fields of destinationaddress in time.

The INZ frame source address holding circuit 43 (INZ-TX-ADRS-B) holds afield of source address (SA) of an INZ frame in an SIG-RV-B signalreceived at the port B.

Further, for a step S02 in FIG. 10,

the condition is checked if an INZ frame reception is detected,reception port B (communication port 11) is blocked, MS port=A is false,and terminal station=not.

At the step S02 in FIG. 10, if the condition is met,

the computer section 30 sets the MS station address to a source address,and holds the reception port B (communication port B) as it is (adaptedto take in a signal through the communication port B).

The computer section 30 turns on the repeat permitting switch 14(SW-FW-B) and the reception permitting switch (SW-RCV-B). That is, areception signal from the communication port B is repeated through therepeat permitting switch 14 (SW-FW-B) to the communication port 10, anda reception signal (SIG-RV-B) from the communication port 11 is input bythe reception permitting switch (SW-RCV-B) to the first-come receptionselecting circuit 20 (RVC-SEL), to determine whether it is a first-comeor not, of which a result is output to the transmission receptioncontrol circuit 21 (MAC/DLC).

Further, the computer section 30 turns the transmission permittingswitch 16 (SW-TX-A) off, and the transmission reception control circuit21 (MAC/DLC) sends an INZ frame (destination is MS station) from the MSport=B (communication port B).

Further, in accordance with an instruction from the computer section 30,the transmission reception control circuit 21 (MAC/DLC) turns thetransmission permitting switch 16 (SW-TX-A) on, rendering a receptionsignal from the port B reception-enabled, to output this to thefirst-come reception selecting circuit 20 (RVC-SEL), to determine if itis a first-come. The CPU in the computer section 30 then sets thestation mode for terminal station to not (negation).

At a step S03 in FIG. 10, if the condition is met, the computer section30 sets the station mode to terminal station STL-T-L, and INZ-COMP=time. . . normal terminal, and goes to sending INZ-COMP frame.

Then, it sets the MS station address to a source address, and holds thereception port B (communication port B) as it is (adapted to take in asignal through the communication port B).

For a step S04 in FIG. 10,

the condition is checked if an INZ frame reception is detected,reception port A (communication port A) is blocked, MS port=B, andterminal station=not.

If this condition is met, it sets the station mode to terminal stationST-T-R, and INZ-COMP=true . . . normal terminal, and goes to sendingINZ-COMP frame.

Next, after the process of step S0, it starts a timer at a step S1 inFIG. 10.

In FIG. 10, the step S102 is a timer starting process.

At the step S102 in FIG. 10, the step S1 is for

responding to a detection of subsequent INZ frame reception from themaster station, by starting the timer to wait for an event of S2.

For the condition: detection of INZ frame reception, station mode beingnot terminal station, INZ-COMP=false, and reception port=A/B, the timeris started.

Thus, it sends initialization-instructing INZ frames in both directions(communication port A, and B), and waits for arrival of a respondingacknowledgment frame (INZ-COMP) from adjacent station.

At this time, the computer section 30 employs the transmission receptioncontrol circuit 21 (MAC/DLC) to render, as illustrated in FIG. 6,blocked state, and reception-prohibited state (SW-TX-A and SW-TX-B to beon) for transmission in both directions.

Then, SW-RCV-A and SW-RCV-B are turned on, for the frame detectiondeterminer 31's INZ-DET-A to detect arrival of an INZ frame in SIG-RV-Areception signal from the communication port A, and INZ-DET-B to detectarrival of an INZ frame in SIG-RV-B reception signal from thecommunication port B

Further, the first-come reception selecting circuit 20 (RCV-SEL)monitors SW-TCV-A and SW-RCV-B, to determine which port has received, ofwhich a result is informed to the transmission reception control circuit21 (MAC/DLC). The reception port that has first received is set as an MSport.

In FIG. 11, the step S103 is a process of setting a transmission stationto a repeater station (an opposing station) or terminal station mode.

After S0 having sent INZ frames, under a condition at S1 detecting forarrival of a subsequent INZ frame, it responds to reception of aresponding acknowledgment INZ frame sent from an adjacent station on anopposite side to the MS port side, by changing a blocked state of thisreception port to the other communication port to an unblocked state,permitting reception of incoming transmission frames to be taken in.

By that, this transmission station has a normal station mode as arepeater station permitting reception of transmission frames received atcommunication ports on bi-directional sides to be taken in, and repeatedto the other sides.

At S21, if the condition: before timer times up, INZ frame receptiondetected, reception port=B, and station mode=not terminal station,

then, it resets timer, setting SW-FW-B on, station mode=normal, and MSport=A.

At S22, if the condition: timer up, INZ frame reception detected,(reception port=B)=false, MS port A, and station mode=not terminalstation,

then, it sets station mode=terminal ST-T-L, MS port=A, INZ-COMP=true . .. anomalous terminal or S04: opposing station.

At S23, if the condition: before timer times up, INZ frame receptiondetected, (reception port=A), MS port B, and station mode=not terminalstation,

then, it resets timer, setting SW-FW-A on, station mode=normal, and MSport=B.

At S24, if the condition: timer up, INZ frame reception detected,(reception port=A)=false), MS port B, and station mode=not terminalstation,

then, it sets station mode=terminal ST-T-R, MS port=B, INZ-COMP=true . .. anomalous terminal or S03: opposing station.

In FIG. 11, the step S104 is a process of determining an R-handedterminal station or an L-handed terminal station. At step S3 in FIG. 11,

that is, it permits an ensured reception of INZ-COMP frame at an MSstation by a sequence of responding acknowledgments with the MS station.This is an embodiment example in which resending processes are continuedup to reception of a responding acknowledgment INZ-COMP frame addressingown station as a destination from the MS station, having differentwaiting times for the resending being ST1 and ST2 depending on stationmodes ST-T-L and ST-T-R, to avoid consecutive overlaps of INZ-COMPframes at the MS station.

In FIG. 11, at the step S3, a completion of initialization is detectedat the MS station side, so it can stop periodically sending INZ frames.

At S31, if the condition: INZ-COMP, and ST-T-L

then, it sets SW-TX-B=OFF, sending INZ-COMP frame (destination=MSstation), station mode=ST-T-L, and

SW-TX-B=ON, starting ST timer (timer value=ST1), INZ-COMP-SENT=true.

At S32, if the condition: INZ-COMP, and ST-T-R

then, it sets SW-TX-A=OFF, sending INZ-COMP frame (destination=MSstation), station mode=ST-T-R, and

SW-TX-A=ON, starting ST timer (timer value=ST2), INZ-COMP-SENT=

In FIG. 11, at the step S105 is a process of resetting timer fordetermination of both terminal stations, and a process of resendingINZ-COMP after a failed transmission.

At S41, if the condition: before ST timer times up, INZ-COMP-REC(INZ-COMP-SENT), INZ-COMP frame reception, destination (own station),and source=MS station,

then, it resets ST timer, as INZ-COMP=false, INZ-COMP-sent=true . . .terminal station fixed, and initializing process ends.

At S42, if the condition: timer up, INZ-COMP-REC=false,

then, INZ-COM frame resending process. Therefore, at a startup such aswhen powered on, even in a network of a plurality of connections, atransmission station automatically stands as an R-handed terminalstation, L-handed terminal station, or repeater station.

1: A transmission station for double-ring networks including a set oftwo or more transmission stations each respectively configured with apair of communication ports for communications to be implementedbi-directionally, and mutually connected by said pairs of communicationports thereof in a ring form through a transmission line to implementintercommunications between transmission stations, characterized in acomplete state of initialization, for each of one or more saidtransmission stations, by: means for periodically sending one or moretransmission frames each respectively containing specific information;for the respective transmission station configured to receivetransmission frames through said pair of communication ports being A andB respectively, by: “SYN frame detecting means A, and -B” for detecting,out of said periodically sent transmission frames, SYN frames havingspecific information meeting set conditions, respectively; “no-SYNdetecting means A, and -B” for detecting no reception of said SYN framesover a preset interval, from output signals of said SYN frame detectingmeans A, and -B, respectively; “SYN absence detecting means” fordetecting, under a condition of periodic SYN frame arrivals through onecommunication port being consecutively continued, absence of periodicarrivals through the other communication port consecutive over a presetinterval; and “reception anomaly detecting means A, and -B” fordetecting anomalies in states of reception signals of transmissionframes received through the communication ports, respectively, and meansfor having a transmission frame as received through either communicationport -A or -B as having detected a no-SYN detecting state by the no-SYNdetecting means A or -B, detected and verified, and responded inaccordance with information contained in said transmission frame, andchanging either as-having-received communication port (as thecommunication port A) to “a blocked state” for said transmission frameto be kept from being repeated to the other communication port (thecommunication port B) to send from the other communication port (thecommunication port B); and means for changing the communication port Aor -B as having detected a reception anomaly detecting state by thereception anomaly detecting means A or -B, to a blocked state, therebyholding communication ports of a plurality of transmission stationsunblocked, on a way from a detection of failure occurrence to a networkfunction recovery by a recovery procedure, and in that: the above-notedfunctions of said terminal station are fulfilled at the plurality oftransmission stations. 2: A communication control method for double ringnetworks including a set of two or more transmission stations eachrespectively configured with a pair of communication ports forcommunications to be implemented bi-directionally, and mutuallyconnected by said pairs of communication ports thereof in a ring formthrough a transmission line to implement intercommunications betweentransmission stations, characterized in a state of configuration fortransmission frames to be kept from continuing circulation in thenetwork of the ring form, by two adjacent terminal stations, with theinitialization completed, under a condition that one or more saidtransmission stations are compliant with a specifically undefinedtransmission line control system for avoiding collisions betweentransmission frames on double ring networks, to send specificinformation-containing one or more transmission frames to beperiodically sent and, among others, above-noted said SYNN frames, andtransmission frames to be sporadically sent, wherein the respectivetransmission station comprises: “RRR frame reception detecting means A,and -B” for detecting reception of RRR frames containing specificcontrol information, respectively; “own address setting” means forsetting information for identification of own station; “adjacent stationaddress setting means A, and -B” for setting information foridentification of transmission stations adjacent to communication portsA, and -B, respectively; “address match detecting means” for detecting amatch by comparison between identification information of own stationand destination information in a received RRR frame from a receptionoutput of either RRR frame reception detecting means; “blocked portresetting means” for responding to a match output of the address matchdetecting means by changing an RRR reception port having received saidRRR frame to an unblocked state; “RRR reception responding means” forresponding to a mismatch output of the address match detecting means byreading identification information of an adjacent transmission stationcorresponding to the RRR reception port from either adjacent stationaddress setting means, to have as a destination to be addressed, andsending an RRR frame generated with the destination, through the RRRreception port, immediately in time for completion of reception of theRRR frame; and “RRR responding acknowledgment means” for detecting bychecking for reception of an RRR frame addressing own station as adestination, within a preset time, following said sending said RRRframe, as an anomaly has occurred in a transmission line or at atransmission station on a route from a transmission station for sendingSYN frames (referred herein to a synchronizing station), thistransmission station being inclusive, with terminal stations inclusive,for a respective transmission station on ways from a location ofoccurrence of anomaly to the terminal stations, by a step of detectingan anomalous state by said no-SYN detecting means and said receptionanomaly detecting means in response to the occurrence of anomaly, andfor a respective transmission station adjacent to the location ofoccurrence of anomaly on routes from the location of occurrence ofanomaly to the synchronizing station, by a step of detecting ananomalous state by the reception anomaly detecting means, whereinas-having-detected communication ports have their status turned toblocked states, respectively, and between said terminal stations beingtwo, for one terminal station in a subsequent position on a route fromthe synchronizing station to the location of occurrence of anomaly, by astep of determining at this terminal station (referred herein to a SYNabsence detecting terminal station) an anomaly as having occurred on theroute to the synchronizing station, from a detection output of theanomalous state by said SYN absence detecting means and a no-SYNdetection output of the SYN absence detecting means, and for the otherterminal station (referred herein to a SYN normal terminal station),which continuous receiving SYN frames normally, by a step of determininga route from this SYN normal terminal station to the synchronizingstation as having a maintained normal communication function, for theSYN absence detecting terminal station, by a step of responding to adetection of occurrence of anomaly of a state of SYN absence from theSYN absence detecting and no-SYN detecting means, by immediately sendingRRR frames addressing the SYN normal terminal station as a destination,through the communication port A, and -B, and a step of waiting, at theRRR responding acknowledgment means, for a response from a transmissionstation adjacent on an opposite side to the SYN normal terminal station,for the SYN normal terminal station, by a step of responding toreception of an RRR frame from the SYN absence detecting terminalstation, as own station is a destination, by changing an RRR receptionport that has been in a blocked state as a terminal station, to anunblocked state by said blocked port resetting means, as the terminalstation status is cancelled, for a respective transmission stationfunctioning normally on a way from the SYN absence detecting terminalstation to the location of occurrence of anomaly, by a step ofresponding to reception of an RRR frame from the SYN absence detectingterminal station, as being not a destination, by sending an RRR framehaving as a destination an adjacent transmission station on the way tothe SYN absence detecting terminal station, by said RRR receptionresponding means, through an RRR reception port, immediately after acompletion of reception of the RRR frame, for the SYN absence detectingterminal station, by a step of responding to reception in time of an RRRframe addressing own station from an adjacent station on the way to thesynchronizing station, by the RRR responding acknowledgment means, bychanging a communication port that has been in a blocked state since thetime of anomaly detection, to an unblocked state, and a step offollowing this changing to change, after lapse of a time the RRRresponding acknowledgment means has preset, also the other communicationport that has been blocked since before as a terminal station, to anunblocked state, thereby canceling the terminal station status, for therespective transmission station functioning normally on the way from theSYN absence detecting terminal station to the location of occurrence ofanomaly, by a step of responding to acknowledgment of reception of anRRR frame addressing own station from the adjacent station on the way tothe synchronizing station, by the RRR responding acknowledgment means,by changing a communication port that has been in a blocked state sincethe time of anomaly detection, to an unblocked state, for a respectivetransmission station adjacent to the location of occurrence of anomalyon ways to SYN absence detecting terminal stations, by a step offollowing absence of reception of an RRR frame addressing own stationover lapse of a preset time, by the RRR responding acknowledgment means,to hold a communication port as it is blocked, to function as a newterminal station, and for occurrence of anomaly at a location adjacentto a SYN absence detecting terminal station, likewise followed byabsence of reception of an RRR frame addressing own station over lapseof a preset time, by the RRR responding acknowledgment means, by a stepof holding a communication port that has been in a blocked state sincethe time of anomaly detection, as it is blocked, and in that the othercommunication port that has been in a blocked state since before as aterminal station is changed to an unblocked state, and as new terminalstations, a terminal station on a way from the anomaly occurrencelocation to the synchronizing station, and a terminal station on anopposite way from the anomaly occurrence location are changed to be newdouble ring network's terminal stations, whereby a network of the ringform is re-configured upon occurrence of communication anomaly. 3: Acommunication control method for double ring networks according to claim2, characterized in a state of configuration for transmission frames tobe kept from continuing circulation in the network of the ring form, bytwo adjacent terminal stations, with the above-noted said initializationcompleted, under a condition that one or more said transmission stationsare compliant with a specifically undefined transmission line controlsystem for avoiding collisions between transmission frames on doublering networks, to send specific information-containing one or moretransmission frames to be periodically sent and, among others,above-noted said SYNN frames, and transmission frames to be sporadicallysent, wherein respective transmission station comprises “own addresssetting” means for setting information for identification of ownstation, and “adjacent station address setting means A, and -B” forsetting information for identification of transmission stations adjacentto communication ports A, and -B, respectively, as an anomaly hasoccurred in a transmission line or at a transmission station on a routefrom a transmission station for sending SYN frames (referred herein to asynchronizing station), this transmission station being inclusive, withterminal stations inclusive, for a respective transmission station onways from a location of occurrence of anomaly to the terminal stations,by a step of detecting an anomalous state by said no-SYN detecting meansand said reception anomaly detecting means in response to the occurrenceof anomaly, and for a respective transmission station adjacent to thelocation of occurrence of anomaly on routes from the location ofoccurrence of anomaly to the synchronizing station, by a step ofdetecting an anomalous state by the reception anomaly detecting means,wherein as-having-detected communication ports have their status turnedto blocked states, respectively, and between said terminal stationsbeing two, for one terminal station in a subsequent position on a routefrom the synchronizing station to the location of occurrence of anomaly,by a step of determining at this terminal station (referred herein to aSYN absence detecting terminal station) an anomaly as having occurred onthe route to the synchronizing station, from a detection output of theanomalous state by said SYN absence detecting means and a no-SYNdetection output of the SYN absence detecting means, and for the otherterminal station (referred herein to a SYN normal terminal station),which continuous receiving SYN frames normally, by a step of determininga route from this SYN normal terminal station to the synchronizingstation as having a maintained normal communication function, for theSYN absence detecting terminal station, by steps of monitoring asequence of transmission frames received from the SYN normal terminalstation, sending specific control information-containing transmissionframes (referred herein to an RRR frame each) addressing the SYN normalterminal station as a destination, at sending timings of transmissionframes assigned to own station in compliance with a transmission linecontrol system for avoiding collisions between transmission frames ondouble ring networks, through the communication port A, and -B, andwaiting for reception of an RRR frame addressing own station as adestination from an adjacent station on the way to the synchronizingstation, for the SYN normal terminal station, by a step of responding toreception of an RRR frame from the SYN absence detecting terminalstation, by comparing own station identification information withdestination information in the received RRR frame, and for a result ofthis comparison that own station is the destination, by a step ofchanging a communication port having received said RRR frame (referredherein to an RRR reception port) that has been in a blocked state sincebefore as a terminal station, to an unblocked state, canceling theterminal station status, for a respective transmission stationfunctioning normally on a way from the SYN absence detecting terminalstation to the location of occurrence of anomaly, by a step ofresponding to reception of an RRR frame from the SYN absence detectingterminal station, by comparing own station identification informationwith destination information in the received RRR frame, and for a resultof this comparison as being not the destination, by a step of sending anRRR frame having as a destination an adjacent transmission station onthe way to the SYN absence detecting terminal station, by said RRRreception responding means, through an RRR reception port, immediatelyafter a completion of reception of the RRR frame, for the SYN absencedetecting terminal station, by a step of responding to reception withina preset time of an RRR frame addressing own station from an adjacentstation on the way to the synchronizing station, by changing acommunication port that has been in a blocked state since the time ofanomaly detection, to an unblocked state, and a step of following thisto change, after lapse of a time the RRR responding acknowledgment meanshas preset, also the other communication port that has been blockedsince before as a terminal station, to an unblocked state, canceling theterminal station status, for the respective transmission stationfunctioning normally on the way from the SYN absence detecting terminalstation to the location of occurrence of anomaly, by a step ofresponding to acknowledgment of reception within a preset time of an RRRframe addressing own station from the adjacent station on the way to thesynchronizing station, by changing a communication port that has been ina blocked state since the time of anomaly detection, to an unblockedstate, for a respective transmission station adjacent to the location ofoccurrence of anomaly on ways to SYN absence detecting terminalstations, by a step of following absence of reception of an RRR frameaddressing own station over lapse of a preset time, by the RRRresponding acknowledgment means, to hold a communication port as it isblocked, to function as a new terminal station, and for occurrence ofanomaly at a location adjacent to a SYN absence detecting terminalstation, likewise followed by absence of reception of an RRR frameaddressing own station over lapse of a preset time, by a step of holdinga communication port that has been in a blocked state since the time ofanomaly detection, as it is blocked, and in that the other communicationport that has been in a blocked state as a terminal station is changedto an unblocked state, and as new terminal stations, a terminal stationon a way from the anomaly occurrence location to the synchronizingstation, and a terminal station on an opposite way from the anomalyoccurrence location are changed to be new double ring network's terminalstations, whereby a network of the ring form is re-configured uponoccurrence of communication anomaly. 4: The communication control methodfor double-ring networks as a reconfiguration method in anomalyoccurrence for double ring networks according to claim 2, wherein as fora format of said transmission frame to be sent and received through saidcommunication ports, and a transmission line interface of saidcommunication ports, it complies with the ISO/IEC8802-3 standard.